COSMOS: 


A  SKETCH 


A  PHYSICAL  DESCRIPTION  OF  THE  UNIVERSE. 


ALEXANDER  VON  HUMBOLDT. 


TKANSLATED  FBOM  THE  GEHMAN, 

BY  E.  C.  OTTE. 


Nataraa  vero  rerum  vis  atquo  majestas  in  omnibus  momentis  fide  caret,  si  quis  modo 
partes  ejus  ac  non  totam  complectatur  animo.— Plin.,  Hist.  Nat.,  lib.  vil,  c.  L 


VOL.  III. 


NEW    YORK: 

HARPER    &    BROTHERS,    PUBLISHERS, 
329   &  331   PEARL   STREET, 

FRANKLIN    SQUARE. 

1858. 


CONTENTS   OF  VOL.   III. 


INTRODUCTION. 

nv 

Historical  Review  of  the  attempts  made  with  the  object  of 
considering  the  Phenomena  of  the  Universe  as  a  Unity 
of  Nature 6-25 


SPECIAL  RESULTS  OF  OBSERVATIONS  IN  THE 
DOMAIN  OF  COSMICAL  PHENOMENA 

A.  URANOLOGICAL  PORTION  of  the  physical  description  of  the 

world.— a.  ASTROGNOSY 26-28 

I.  The  realms  of  space,  and  conjectures  regarding  that  which 

appears  to  occupy  the  space  intervening  between  the 
heavenly  bodies 29-41 

II.  Natural  and  telescopic  vision,  41-73  ;  Scintillation  of  the 

stars,  73-83 ;  Velocity  of  light,  83-89  ;  Results  of  pho- 
tometry, 89-102  41-102 

III.  Number,  distribution,  and  color  of  the  fixed  stars,  103- 

139;  Stellar  masses  (stellar  swarms),  139-143;  The 
Milky  Way  interspersed  with  a  few  nebulous  spots, 
143-151  103-151 

IV.  New  stars,  and  stars  that  have  vanished,  151-160 ;  Va- 

riable stars,  whose  recurring  periods  have  been  determ- 
ined, 160-177;  Variations  in  the  intensity  of  the  light 
of  stars  whose  periodicity  is  as  yet  uninvestigated,  177- 
182  151-182 

V.  Proper  motion  of  the  fixed  stars,  182-185  ;  Problemat- 

ical existence  of  dark  cosmical  bodies,  185-188  ;  Par- 
allax— measured  distances  of  some  of  the  fixed  stars, 
188-194;  Doubts  as  to  the  assumption  of  a  central 
body  for  the  whole  sidereal  heavens,  194-199 182-199 

VI.  Multiple,  or  double  stars — Their  number  and  reciprocal 

distances. — Period  of  revolution  of  two  stars  round  a 
common  center  of  gravity 199-21.* 


IV  CONTENTS. 

TABLES. 

Fag. 

Photometric  Tables  of  Stars 100-102 

Clusters  of  Stars 141-143 

New  Stars 155-160 

Variable  Stars 172-177 

Parallaxes 193 

Elements  of  Orbits  of  double  Stars ...  213 


SPECIAL  RESULTS  OF  OBSERVATION 

IN   THE 

DOMAIN  OF  COSMICAL  PHENOMENA. 


INTRODUCTION. 

IN  accordance  with  the  object  I  have  proposed  to  myself, 
and  which,  as  far  as  my  own  powers  and  the  present  stata 
of  science  permit,  I  have  regarded  as  not  unattainable,  I 
have,  in  the  preceding  volumes  of  Cosmos,  considered  Nature 
in  a  two-fold  point  of  view.  In  the  first  place,  I  have  en- 
deavored to  present  her  in  the  pure  objectiveness  of  external 
phenomena  ;  and,  secondly,  as  the  reflection  of  the  image  im- 
pressed by  the  senses  upon  the  inner  man,  that  is,  upon  his 
ideas  and  feelings. 

The  external  world  of  phenomena  has  been  delineated  un- 
der the  scientific  form  of  a  general  picture  of  nature  in  her 
two  great  spheres,  the  uranological  and  the  telluric  or  ter- 
restrial. This  delineation  begins  with  the  stars,  which  glim- 
mer amid  nebulae  in  the  remotest  realms  of  space,  and,  pass- 
ing from  our  planetary  system  to  the  vegetable  covering  of 
the  earth,  descends  to  the  minutest  organisms  which  float  in 
the  atmosphere,  and  are  invisible  to  the  naked  eye.  In  order 
to  give  due  prominence  to  the  consideration  of  the  existence 
of  one  common  bond  encircling  the  whole  organic  world,  of 
the  control  of  eternal  laws,  and  of  the  causal  connection,  as 
far  as  yet  known  to  us,  of  whole  groups  of  phenomena,  it  was 
necessary  to  avoid  the  accumulation  of  isolated  facts.  This 
precaution  seemed  especially  requisite  where,  in  addition  to 
the  dynamic  action  of  moving  forces,  the  powerful  influence 
of  a  specific  difference  of  matter  manifests  itself  in  the  ter- 
restrial portion  of  the  universe.  Tho  problems  presented  to 
us  in  the  sidereal,  or  uranological  sphere  of  the  Cosmos,  are, 
considering  their  nature,  in  as  far  as  they  admit  of  being  ob- 
served, of  extraordinary  simplicity,  and  capable,  by  means  of 
the  attractive  force  of  matter  and  the  quantity  of  its  mass, 
of  being  submitted  to  exact  calculation  in  accordance  with 


the  theory  of  motion.  If,  as  I  believe,  we  are  justified  in  re- 
garding the  revolving  meteor-asteroids  (aerolites)  as  portions 
of  our  planetary  system,  their  fall  upon  the  earth  constitutes 
the  sole  means  by  which  we  are  brought  in  contact  with 
cosmical  substances  of  a  recognizable  heterogeneity.*  I  here 
refer  to  the  cause  which  has  hitherto  rendered  terrestrial 
phenomena  less  amenable  to  th  rules  of  mathematical  de- 
duction than  those  mutually  disturbing  and  readjusting  move- 
ments of  the  cosmical  bodies,  in  which  the  fundamental  force 
of  homogeneous  matter  is  alone  manifested. 

I  have  endeavored,  in  my  delineation  of  the  earth,  to  ar- 
range natural  phenomena  in  such  a  manner  as  to  indicate 
their  causal  connection.  In  describing  our  terrestrial  sphere, 
I  have  considered  its  form,  mean  density,  electro-magnetic 
currents,  the  processes  of  polar  light,  and  the  gradations  ac- 
cording to  which  heat  increases  with  the  increase  of  depth. 
The  reaction  of  the  planet's  interior  on  its  outer  crust  im- 
plies the  existence  of  volcanic  activity  ;  of  more  or  less  con- 
tracted circles  of  waves  of  commotion  (earthquake  waves), 
and  their  effects,  which  are  not  always  purely  dynamic  ;  and 
of  the  eruptions  of  gas,  of  mud,  and  of  thermal  springs.  The 
upheaval  of  fire-erupting  mountains  must  be  regarded  as  the 
highest  demonstration  of  the  inner  terrestrial  forces.  We 
have  therefore  depicted  volcanoes,  both  central  and  chain 
formations,  as  generative  no  less  than  as  destructive  agents, 
and  as  constantly  forming  before  our  eyes,  for  the  most  part, 
periodic  rocks  (rocks  of  eruption)  ;  we  have  likewise  shown, 
in  contrast  with  this  formation,  how  sedimentary  rocks  are 
in  the  course  of  precipitation  from  fluids,  which  hold  their 
minutest  particles  in  solution  or  suspension.  Such  a  com- 
parison of  matter  still  in  the  act  of  development  and  solidi- 
fication with  that  already  consolidated  in  the  form  of  strata 
of  the  earth's  crust,  leads  us  to  the  distinction  of  geognostic 
epochs,  and  to  a  more  certain  determination  of  the  chronolog- 
ical succession  of  those  formations  in  which  lie  entombed  ex- 
tinct genera  of  animals  and  plants — the  fauna  and  flora  of  a 
former  world,  whose  ages  are  revealed  by  the  order  in  which 
they  occur.  The  origin,  ransformation,  and  upheaval  of  ter- 
restrial strata,  exert,  at  certain  epochs,  an  alternating  actior 
on  all  the  special  characteristics  of  the  physical  configura 
tion  of  the  earth's  surface  ;  influencing  the  distribution  of 
fluids  and  solids,  and  the  extension  and  articulation  of  con 

•  Cotmos,  vol.  i.  (Harper's  edit.),  p   33-65,  136. 


INTRODUCTION.  7 

tinental  masses  in  a  horizontal  and  vertical  direction.  On 
these  relations  depend  the  thermal  conditions  of  oceanic  cur- 
rents, the  meteorological  processes  in  the  aerial  investment 
of  our  planet,  and  the  typical  and  geographical  distribution 
of  organic  forms.  Such  a  reference  to  the  arrangement  of 
telluric  phenomena  presented  in  the  picture  of  nature,  will, 
I  think,  suffice  to  show  that  the  juxtaposition  of  great,  and 
apparently  complicated,  results  of  observation,  facilitates  our 
insight  into  their  causal  connection.  Our  impressions  of  na- 
ture will,  however,  be  essentially  weakened,  if  the  picture 
fail  in  warmth  of  color  by  the  too  great  accumulation  of 
minor  details. 

In  a  carefully-sketched  representation  of  the  phenomena 
of  the  material  world,  completeness  in  the  enumeration  of 
individual  features  has  not  been  deemed  essential,  neither 
does  it  seem  desirable  in  the  delineation  of  the  reflex  of  ex- 
ternal nature  on  the  inner  man.  Here  it  was  necessary  to 
observe  even  stricter  limits.  The  boundless  domain  of  the 
world  of  thought,  enriched  for  thousands  of  years  by  the  vig- 
orous force  of  intellectual  activity,  exhibits,  among  different 
races  of  men,  and  in  different  stages  of  civilization,  sometimes 
a  joyous,  sometimes  a  melancholy  tone  of  mind  ;*  sometimes 
a  delicate  appreciation  of  the  beautiful,  sometimes  an  apa- 
thetic insensibility.  The  mind  of  man  is  first  led  to  adore 
the  forces  of  nature  and  certain  objects  of  the  material  world  ; 
at  a  later  period  it  yields  to  religious  impulses  of  a  higher 
and  purely  spiritual  character.!  The  inner  reflex  of  the 
outer  world  exerts  the  most  varied  influence  on  the  myste- 
rious process  of  the  formation  of  language, $  in  which  the 
original  corporeal  tendencies,  as  well  as  the  impressions  of 
surrounding  nature,  act  as  powerful  concurring  elements. 
Man  elaborates  within  himself  the  materials  presented  to 
him  by  the  senses,  and  the  products  of  this  spiritual  labo- 
belong  as  essentially  to  the  domain  of  the  COSMOS  as  do  the 
phenomena  of  the  external  world. 

As  a  reflected  image  of  Nature,  influenced  by  the  crea- 
tions of  excited  imagination,  can  not  retain  its  truthful  purity, 
there  has  arisen,  besides  the  actual  and  external  world,  an 
ideal  and  internal  world,  full  of  fantastic  and  partly  sym- 
bolical myths,  heightened  by  the  introduction  of  fabulous  ani- 
mal forms,  whose  several  parts  are  derived  from  the  organ- 

*  Cosmos,  vol.  i.,  p.  23-25  ;  vol.  ii.,  p.  25  and  97. 

t  Ibid.,  vol.  ii.,  p.  38-43,  and  56-60. 

\  Ibid,  vol.  i.,  p.  357-359;  vol.  ii.,  p.  112-117. 


8  COSMOS. 

isms  of  the  present  world,  and  sometimes  even  from  the  relics 
of  extinct  species.*  Marvelous  flowers  and  trees  spring  from 
this  mythic  soil,  as  the  giant  ash  of  the  Edda-Songs,  the 
world-tree  Yggdrasil,  whose  branches  tower  above  the  heav- 
ens, while  one  of  its  triple  roots  penetrates  to  the  "  foaming 
caldron  springs"  of  the  lower  world. t  Thus  the  cloud-re- 
gion of  physical  myths  is  filled  with  pleasing  or  with  fearful 
forms,  according  to  the  diversity  of  character  in  nations  and 
climates  ;  and  these  forms  are  preserved  for  centuries  in  the 
intellectual  domain  of  successive  generations. 

If  the  present  work  does  not  fully  bear  out  its  title,  the 
adoption  of  which  I  have  myself  designated  as  bold  and  in- 
considerate, the  charge  of  incompleteness  applies  especially 
to  that  portion  of  the  COSMOS  which  treats  of  spiritual  life  ; 
that  is,  the  image  reflected  by  external  nature  on  the  inner 
world  of  thought  and  feeling.  In  this  portion  of  my  work  I 
have  contented  myself  with  dwelling  more  especially  upon 
those  objects  which  lie  in  the  direction  of  long-cherished 
studies  ;  on  the  manifestation  of  a  more  or  less  lively  appre- 
ciation of  nature  in  classical  antiquity  and  in  modern  times  ; 
on  the  fragments  of  poetical  descriptions  of  nature,  the  col- 
oring of  which  has  been  so  essentially  influenced  by  individ- 
uality of  national  character,  and  the  religious  monotheistic 
view  of  creation ;  on  the  fascinating  charm  of  landscape 
painting  ;  and  on  the  history  of  the  contemplation  of  the 
physical  universe,  that  is,  the  history  of  the  recognition  of 
the  universe  as  a  whole,  and  of  the  unity  of  phenomena — a 
recognition  gradually  developed  during  the  course  of  two 
thousand  years. 

In  a  work  of  so  comprehensive  a  character,  the  object  of 
which  is  to  give  a  scientific,  and,  at  the  same  time,  an  ani- 
mated description  of  nature,  a  first  imperfect  attempt  must 
rather  lay  claim  to  the  merit  of  inciting  than  to  that  of  sat- 
isfying inquiry.  A  Book  of  Nature,  worthy  of  its  exalted 
title,  can  nerer  be  accomplished  until  the  physical  sciences, 
notwithstanding  their  inherent  imperfectibility,  shall,  by  theii 

*  M.  von  Olfer's  Ueberreste  vorweltlicher  Riesenthiere  in  Beziehung  auj 
Ostasiatische  Sagen  in  the  Abh.  der  Berl.  ATead.,  1832,  s.  51.  On  the 
opinion  advanced  by  Empedocles  regarding  the  cause  of  the  extinction 
of  the  earliest  animal  forms,  see  Hegel's  Geschichte  der  Philosophic, 
bd.  ii.,  8.  344. 

t  See,  for  the  world-tree  Yggdrasil,  and  the  rushing  (foaming)  cal- 
dron-spring Hvergelmir,  the  Deutsche  Mylhologie  of  Jacob  Grimm,  1844, 
B.  530,  756;  also  Mallet's  Northern  Antiquities  (Bohn's  edition),  1847 
p.  410,  489,  aud  492,  and  frontispiece  to  ditto. 


INTRODUCTION.  9 

gradual  development  and  extension,  have  attained  a  higher 
degree  of  advancement,  and  until  we  shall  have  gained  a 
more  extended  knowledge  of  the  two  grand  divisions  of  the 
COSMOS  —  the  external  world,  as  made  perceptible  to  us  by 
the  senses  ;  and  the  inner,  reflected  intellectual  world. 

I  think  I  have  here  sufficiently  indicated  the  reasons  which 
determined  me  not  to  give  greater  extension  to  the  general 
picture  of  nature.  It  remains  for  this  third  and  fourth  volume 
of  my  Cosmos  to  supply  much  that  is  wanting  in  the  previ- 
ous portions  of  the  work,  and  to  present  those  results  of  ob- 
servation on  which  the  present  condition  of  scientific  opinion 
is  especially  grounded.  I  shall  here  follow  a  similar  mode 
of  arrangement  to  that  previously  adopted,  for  the  reasons 
which  I  have  advanced,  in  the  delineation  of  nature.  But, 
before  entering  upon  the  individual  facts  on  which  special 
departments  of  science  are  based,  I  would  fain  offer  a  few 
more  general  explanatory  observations.  The  unexpected  in- 
dulgence with  which  my  undertaking  has  been  received  by 
a  large  portion  of  the  public,  both  at  home  and  abroad,  ren- 
ders it  doubly  imperative  that  I  should  once  more  define,  as 
distinctly  as  possible,  the  fundamental  ideas  on  which  the 
whole  work  is  based,  and  say  something  in  regard  to  those 
demands  which  I  have  not  even  attempted  to  satisfy,  be- 
cause, according  to  my  view  of  empirical — i.  e.,  experiment- 
al— science,  they  did  not  admit  of  being  satisfied.  These 
explanatory  observations  involuntarily  associate  themselves 
with  historical  recollections  of  the  earlier  attempts  made  to 
discover  the  one  universal  idea  to  which  all  phenomena,  in 
their  causal  connection,  might  be  reduced,  as  to  a  sole  prin- 
ciple. 

The  fundamental  principle*  of  my  work  on  the  COSMOS, 
as  enunciated  by  me  more  than  twenty  years  ago,  in  the 
French  and  German  lectures  I  gave  at  Paris  and  Berlin, 
comprehended  the  endeavor  to  combine  all  cosmical  phenom- 
ena in  one  sole  picture  of  nature  ;  to  show  in  what  manner 
the  common  conditions,  that  is  to  say,  the  great  laws,  by 
which  individual  groups  of  these  phenomena  are  governed, 
have  been  recognized  ;  and  what  course  has  been  pursued 
in  ascending  from  these  laws  to  the  discovery  of  their  causal 
connection.  Such  an  attempt  to  comprehend  the  plan  of 
the  universe — the  order  of  nature — must  begin  with  a  gen« 
eralization  of  particular  facts,  and  a  knowledge  of  the  con- 

*  Cotmot.  vol.  i.,  p.  48-50,  and  68-77. 


10  COSMOS. 

ditions  under  which  physical  changes  regularly  and  period- 
ically manifest  themselves  ;  and  must  conduct  to  the  thought- 
ful consideration  of  the  results  yielded  by  empirical  observa- 
tion, but  not  to  "  a  contemplation  of  the  universe  based  on 
speculative  deductions  and  development  of  thought  alone,  or 
to  a  theory  of  absolute  unity  independent  of  experience." 
We  are,  I  here  repeat,  far  distant  from  the  period  when  it 
was  thought  possible  to  concentrate  all  sensuous  perceptions 
into  the  unity  of  one  sole  idea  of  nature.  The  true  path  was 
indicated  upward  of  a  century  before  Lord  Bacon's  time,  by 
Leonardo  da  Vinci,  in  these  lew  words  :  "  Cominciare  dall' 
esperienza  e  per  mezzo  di  questa  scoprirne  la  ragione."* 
"  Commence  by  experience,  and  by  means  of  this  discover 
the  reason."  In  many  groups  of  phenomena  we  must  still 
content  ourselves  with  the  recognition  of  empirical  laws  ;  but 
the  highest  and  more  rarely  attained  aim  of  all  natural  in- 
quiry must  ever  be  the  discovery  of  their  causal  connection. t 
The  most  satisfactory  and  distinct  evidence  will  always  ap- 
pear where  the  laws  of  phenomena  admit  of  being  referred 
to  mathematical  principles  of  explanation.  Physical  cosmog- 
raphy constitutes  merely  in  some  of  its  parts  a  cosmology. 
The  two  expressions  can  not  yet  be  regarded  as  identical. 
The  great  and  solemn  spirit  that  pervades  the  intellectual 

*  Op.  tit.,  vol.  ii.  p.  283. 

t  In  the  Introductory  Observations,  in  Cosmos,  vol.  i.,  p.  50,  it  should 
not  have  been  generally  stated  that  "  the  ultimate  object  of  the  experi- 
mental sciences  is  to  discover  laws,  and  to  trace- their  progressive  gen- 
eralization." The  clause  "  in  many  kinds  of  phenomena"  should  have 
been  added.  The  caution  with  which  I  have  expressed  myself  in  the 
second  volume  of  this  work  (p.  313),  on  the  relation  borne  by  Newton 
to  Kepler,  can  not,  I  think,  leave  a  doubt  that  I  clearly  distinguish  be- 
tween the  discovery  and  interpretation  of  natural  laws,  i.e.,  the  explana- 
tion of  phenomena.  I  there  said  of  Kepler:  "  The  rich  abundance  of 
accurate  observations  furnished  by  Tycho  Brahe,  the  zealous  opponent 
of  the  Copernican  system,  laid  the  foundation  for  the  discovery  of  those 
eternal  laws  of  the  planetary  movements  which  prepared  imperishable 
renown  for  the  name  of  Kepler,  and  which,  interpreted  by  Newton, 
and  proved  to  be  theoretically  and  necessarily  true,  have  been  transferred 
into  the  bright  and  glorious  domaiu  of  thought,  as  the  intellectual  rec- 
ognition of  nature."  Of  Newton  I  said  (p.  351):  "We  close  it  [the 
great  epoch  of  Galileo,  Kepler,  Newton,  and  Leibnitz]  with  the  figure 
of  the  earth  as  it  was  then  recognized  from  theoretical  conclusions.  New- 
ton was  enabled  to  give  an  explanation  of  the  system  of  the  universe, 
because  he  succeeded  in  discovering  the  force  from  whose  action  the 
laws  of  Kepler  necessarily  result."  Compare  on  this  subject  ("  On  Laws 
and  Causes")  the  admirable  remarks  in  Sir  John  Herschel's  address  at 
the  fifteenth  meeting  of  the  British  Association  at  Cambridge,  1845,  p. 
rlii. ;  and  Edinb.  Rev.,  vol.  87,  1848,  p.  180-183. 


INTRODUCTION.  11 

labor,  of  which  the  limits  are  here  defined,  arises  from  the 
sublime  consciousness  of  striving  toward  the  infinite,  and  of 
grasping  all  that  is  revealed  to  us  amid  the  boundless  and 
inexhaustible  fullness  of  creation,  development,  and  being. 

This  active  striving,  which  has  existed  in  all  ages,  must 
frequently,  and  under  various  forms,  have  deluded  men  into 
the  idea  that  they  had  reached  the  goal,  and  discovered  the 
principle  which  could  explain  all  that  is  variable  in  the  or- 
ganic world,  and  all  the  phenomena  revealed  to  us  by  sen- 
suous perception.  After  men  had  for  a  long  time,  in  accord- 
ance with  the  earliest  ideas  of  the  Hellenic  people,  vener- 
ated the  agency  of  spirits,  embodied  in  human  forms,*  in  the 
creative,  changing,  and  destructive  processes  of  nature,  the 
germ  of  a  scientific  contemplation  developed  itself  in  the 
physiological  fancies  of  the  Ionic  school.  The  first  principle 
of  the  origin  of  things,  the  first  principle  of  all  phenomena, 
was  referred  to  two  causes! — either  to  concrete  material  prin- 
ciples, the  so-called  elements  of  Nature,  or  to  processes  of 
rarefaction  and  condensation,  sometimes  in  accordance  with 
mechanical,  sometimes  with  dynamic  views.  The  hypothe- 
sis of  four  or  five  materially  differing  elements,  which  was 
probably  of  Indian  origin,  has  continued,  from  the  era  of  the 
didactic  poem  of  Empedocles  down  to  the  most  recent  times, 
to  imbue  all  opinions  on  natural  philosophy — a  primeval  evi- 
dence and  monument  of  the  tendency  of  the  human  mind 
to  seek  a  generalization  and  simplification  of  ideas,  not  only 
with  reference  to  the  forces,  but  also  to  the  qualitative  na- 
ture of  matter. 

In  the  latter  period  of  the  development  of  the  Ionic  phys- 
iology, Anaxagoras  of  Clazomense  advanced  from  the  postu- 
late of  simply  dynamic  forces  of  matter  to  the  idea  of  a  spirit 
independent  of  all  matter,  uniting  and  distributing  the  homo- 
geneous particles  of  which  matter  is  composed.  The  world- 
arranging  Intelligence  (vovg)  controls  the  continuously  pro- 
gressing formation  of  the  world,  and  is  the  primary  source 

*  In  the  memorable  passage  (Metaph.,  xii.,  8,  p.  1074,  Bekker")  in 
which  Aristotle  speaks  of  "  the  relics  of  an  earlier  acquired  and  subse- 
quently lost  wisdom,"  he  refers  with  extraordinary  freedom  and  sig- 
nificance to  the  veneration  of  physical  forces,  and  of  gods  in  human 
forms :  "  much,"  says  he,  "  has  been  mythically  added  for  the  persua* 
tion  of  the  multitude,  as  also  on  account  of  the  laws  and  for  other  useful 
ends." 

t  The  important  difference  in  these  philosophical  directions  rpdiroi, 
is  clearly  indicated  in  Arist.,  Phys.  Auscult.,  1,  4,  p.  187,  Bekk.  (Com- 
pare  Brandis,  in  the  Rhein.  Museum  fur  Philologie,  Jahrg.  iii.,  8.  105.) 


12  COSMOS. 

of  all  motion,  and  therefore  of  all  physical  phenomena.  An- 
axagoras  explains  the  apparent  movement  of  the  heavenly 
bodies  from  east  to  west  by  the  assumption  of  a  centrifugal 
force,*  on  the  intermission  of  which,  as  we  have  already  ob- 
served, the  fall  of  meteoric  stones  ensues.  This  hypothesis 
indicates  the  origin  of  those  theories  of  rotatory  motion  which 
more  than  two  thousand  years  afterward  attained  considera- 
ble cosmical  importance  from  the  labors  of  Descartes,  Huy- 
gens,  and  Hooke.  It  would  be  foreign  to  the  present  work 
to  discuss  whether  thg  world- arranging  Intelligence  of  the 
philosopher  of  Clazomenae  indicates!  the  Godhead  itself,  or 
the  mere  pantheistic  notion  of  a  spiritual  principle  animating 
all  nature. 

In  striking  contrast  with  these  two  divisions  of  the  Ionic 
school  is  the  mathematical  symbolism  of  the  Pythagoreans, 
which  in  like  manner  embraced  the  whole  universe.  Here, 
in  the  world  of  physical  phenomena  cognizable  by  the  senses, 
the  attention  is  solely  directed  to  that  which  is  normal  in  con- 
figuration (the  five  elementary  forms),  to  the  ideas  of  num- 
bers, measure,  harmony,  and  contrarieties.  Things  are  re- 
flected in  numbers  "which  are,  as  it  were,  an  imitative  repre- 
sentation (fj,ifj,7)aig)  of  them.  The  boundless  capacity  for  rep- 
etition, and  the  illimitability  of  numbers,  is  typical  of  the 
character  of  eternity  and  of  the  infinitude  of  nature.  The 
essence  of  things  may  be  recognized  in  the  form  of  numerical 
relations ;  their  alterations  and  metamorphoses  as  numerical 
combinations.  Plato,  in  his  Physics,  attempted  to  refer  the 
nature  of  all  substances  in  the  universe,  and  their  different 
stages  of  metamorphosis,  to  corporeal  forms,  and  these,  again, 
to  the  simplest  triangular  plane  figures. J  But  in  reference 

*  Cosmos,  vol.  i.,  p.  133-135  (note),  and  vol.  ii.,  p.  309,  310  (and 
note).  Simplicius,  in  a  remarkable  passage,  p.  491,  most  distinctly 
contrasts  the  centripetal  with  the  centrifugal  force.  He  there  says, 
"  The  heavenly  bodies  do  not  fall  in  consequence  of  the  centrifugal  force 
being  superior  to  the  inherent  falling  force  of  bodies  and  to  their  down- 
ward tendency."  Hence  Plutarch,  in  his  work,  De  Fade  in  Orbe 
Ltmte,  p.  923,  compares  the  moon,  in  consequence  of  its  not  falling  to 
the  earth,  to  "  a  stone  in  a  sling."  For  the  actual  signification  of  the 
•nepiXupT)ai.s  of  Anaxagoras,  compare  Schaubach,  in  Anaxag.  Clazom. 
Fragm.,  1827,  p.  107-109. 

t  Schaubach,  Op.  cit.,  p.  151-156,  and  185-189.  Plants  are  likewise 
said  to  be  animated  by  the  intelligence  i>ot5f  ;  Aristot.,  De  Plant.,  i.,  p. 
815,  Bekk. 

t  Compare,  on  this  portion  of  Plato's  mathematical  physics,  B6ckh, 
De  Platonico  Syst.  Caelestium  Globorum,  1810  et  1811;  Martin,  Eludei 
tur  le  Timie,  torn,  ii.,  p.  234-242;  and  Brandis,  in  the  Geschichte  der 
GricchiKh-Rdmuchsn  Philosophic,  th.  ii.,  abth.  i.,  1844,  $  375. 


INTRODUCTION.  13 

to  ultimate  principles  (the  elements,  as  it  were,  of  the  ele 
ments),  Plato  exclaims,  with  modest  diffidence1,  "  God  alone, 
and  those  whom  he  loves  among  men,  know  what  they  are." 
Such  a  mathematical  mode  of  treating  physical  phenomena, 
together  with  the  development  of  the  atomic  theory,  and  the 
philosophy  of  measure  and  harmony,  have  long  obstructed  the 
development  of  the  physical  sciences,  and  misled  fanciful  in- 
quirers into  devious  tracks,  as  is  shown  in  the  history  of  the 
physical  contemplation  of  the  universe.  "  There  dwells  a 
captivating  charm,  celebrated  by  all  antiquity,  in  the  simple 
relations  of  time  and  space,  as  manifested  in  tones,  numbers, 
and  lines."* 

The  idea  of  the  harmonious  government  of  the  universe  re- 
veals itself  in  a  distinct  and  exalted  tone  throughout  the  writ- 
ings of  Aristotle.  All  the  phenomena  of  nature  are  depicted 
in  the  Physical  Lectures  (Auscultationes  Physicce)  as  mov- 
ing, vital  agents  of  one  general  cosmical  force.  Heaven  and 
nature  (the  telluric  sphere  of  phenomena)  depend  upon  the 
"  unmoved  motus  of  the  universe."!  The  "  ordainer"  and  the 
ultimate  cause  of  all  sensuous  changes  must  be  regarded  as 
something  non-sensuous  and  distinct  from  all  matter.^  Unity 
in  the  different  expressions  of  material  force  is  raised  to  the 
rank  of  a  main  principle,  and  these  expressions  of  force  are 
themselves  always  reduced  to  motions.  Thus  we  find  already 
in  "  the  book  of  the  soul"§  the  germ  of  the  undulatory  theory 
of  light.  The  sensation  of  sight  is  occasioned  by  a  vibration 

*  Cosmos,  vol.  ii.,  p.  351,  note.  Compare  also  Gruppe,  Ueber  die 
Fragmente  des  Archytas,  1840,  s.  33. 

t  Aristot.,Poto.,  vii.,  4, p.  1326,  and  Metapk.,  xii.,  7,  p.  1072, 10,  Bekk., 
and  xii.,  10,  p.  1074-5.  The  pseudo-Aristotelian  work,  De  Mundo, 
which  Osann  ascribed  to  Chrysippus  (see  Cotmot,  vol.  ii.,  p.  28,  29), 
also  contains  (cap.  6,  p.  397)  a  very  eloquent  passage  on  the  world-or- 
derer  and  tcorld-sustainer. 

t  The  proofs  are  collected  in  Ritter,  History  of  Philotophy  (Bohn, 
1838-46),  vol.  iii.,  p.  180,  et  seq. 

§  Compare  Aristot.,  De  Anima,  ii.,  7,  p.  419.  In  this  passage  the 
analogy  with  sound  is  most  distinctly  expressed,  although  in  other  por- 
tions of  his  writings  Aristotle  has  greatly  modified  his  theory  of  vision. 
Thus,  in  De  Insomniis,  cap.  2,  p.  459,  Bekker,  we  find  the  following 
words :  "  It  is  evident  that  sight  is  no  less  an  active  than  a  passive 
agent,  and  that  vision  not  only  experiences  some  action  from  the  air 
(the  medium),  but  itself  also  acts  upon  the  medium."  He  adduces  in 
evidence  of  the  truth  of  this  proposition,  that  a  new  and  very  pure  me- 
tallic mirror  will,  under  certain  conditions,  when  looked  at  by  a  woman, 
retain  on  its  surface  cloudy  specks  that  can  not  be  removed  without 
difficulty.  Compare  also  Martin,  Etudes  sur  le  Timfe  de  Platun.,  torn 
ii.  p.  159-163. 


14  COSMOS. 

— a  movement  of  the  medium  between  the  eye  and  the  object 
Been — and  not  by  emissions  from  the  object  or  the  eye.  Hear- 
ing is  compared  with  sight,  as  sound  is  likewise  a  consequence 
of  the  vibration  of  the  air. 

Aristotle,  while  he  teaches  men  to  investigate  generalities 
in  the  particulars  of  perceptible  unities  by  the  force  of  reflect- 
ive reason,  always  includes  the  whole  of  nature,  and  the  in- 
ternal connection  not  only  of  forces,  but  also  of  organic  forms. 
In  his  book  on  the  parts  (organs)  of  animals,  he  clearly  in- 
timates his  belief  that  throughout  all  animate  beings  there  is 
a  scale  of  gradation,  in  which  they  ascend  from  lower  to  high- 
er forms.  Nature  advances  in  an  uninterrupted  progressive 
course  of  development,  from  the  inanimate  or  "  elementary" 
to  plants  and  animals ;  and,  "  lastly,  to  that  which,  though 
not  actually  an  animal,  is  yet  so  nearly  allied  to  one,  that  on 
the  whole  there  is  little  difference  between  them."*  In  the 
transition  of  formations,  "  the  gradations  are  almost  imper- 
ceptible."! The  unity  of  nature  was  to  the  Stagirite  the  great 
problem  of  the  Cosmos.  "  In  this  unity,"  he  observes,  with 
singular  animation  of  expression,  "  there  is  nothing  unconnect- 
ed or  out  of  place,  as  in  a  bad  tragedy."}: 

The  endeavor  to  reduce  all  the  phenomena  of  the  universe 
to  one  principle  of  explanation  is  manifest  throughout  the 
physical  works  of  this  profound  philosopher  and  accurate  ob- 
server of  nature  ;  but  the  imperfect  condition  of  science,  and 
ignorance  of  the  mode  of  conducting  experiments,  i.  e.,  of 
calling  forth  phenomena  under  definite  conditions,  prevented 
the  comprehension  of  the  causal  connection  of  even  small 
groups  of  physical  processes.  All  things  were  reduced  to  the 
ever-recurring  contrasts  of  heat  and  cold,  moisture  and  dry- 
ness,  primary  density  and  rarefaction — even  to  an  evolution 
of  alterations  in  the  organic  world  by  a  species  of  inner  divis- 
ion (antiperistasis),  which  reminds  us  of  the  modern  hypothesis 
of  opposite  polarities  and  the  contrasts  presented  by  +  and  —  .§ 

*  Aristot.,  De  partibus  Amm.,  lib.  iv.,  cap.  5,  p.  681,  lin.  12,  Bekker. 

t  Aristot.,  Hist.  Anim.,  lib.  ix.,  cap.  1,  p.  588,  lin.  10-24,  Bekker. 
When  any  of  the  representatives  of  the  four  elements  in  the  animal 
kingdom  on  oar  globe  fail,  as,  for  instance,  those  which  represent  the 
element  of  the  purest  fire,  the  intermediate  stages  may  perhaps  be  found 
to  occur  in  the  moon.  (Biese,  Die  Phil,  des  Aristoteles,  bd.  ii.,  s.  186.) 
It  is  singular  enough  that  the  Stagirite  should  seek  in  another  planet 
those  intermediate  links  of  the  chain  of  organized  beings  which  we  find 
in  the  extinct  animal  and  vegetable  forms  of  an  earlier  world. 

t  Aristot.,  Metaph.,  lib.  xiii.,  cap.  3,  p.  1090,  lin.  20,  Bekker. 

§  The  uvrnrepiiraait  of  Aristotle  plays  an  important  part  in  all  hit 


INTRODUCTION.  15 

The  so-calle"d  solutions  of  the  problems  only  reproduce  the 
same  facts  in  a  disguised  form,  and  the  otherwise  vigorous 
and  concise  style  of  the  Stagirite  degenerates  in  his  explana- 
tions of  meteorological  or  optical  processes  into  a  self-com- 
placent diffuseness  and  a  somewhat  Hellenic  verbosity.  As 
Aristotle's  inquiries  were  directed  almost  exclusively  to  mo- 
tion, and  seldom  to  differences  in  matter,  we  find  the  funda- 
mental idea,  that  all  telluric  natural  phenomena  are  to  be 
ascribed  to  the  impulse  of  the  movement  of  the  heavens — 
the  rotation  of  the  celestial  sphere  —  constantly  recurring, 
fondly  cherished  and  fostered,*  but  never  declared  with  ab- 
solute distinctness  and  certainty. 

The  impulse  to  which  I  refer  indicates  only  the  communi- 
cation of  motion  as  the  cause  of  all  terrestrial  phenomena. 
Pantheistic  views  are  excluded ;  the  Godhead  is  considered 
as  the  highest  "ordering  unity,  manifested  in  all  parts  of  the 
universe,  defining  and  determining  the  nature  of  all  forma- 
tions, and  holding  together  all  things  as  an  absolute  power.f 
The  main  idea  and  these  teleological  views  are  not  applied 
to  the  subordinate  processes  of  inorganic  or  elementary  nature, 
but  refer  specially  to  the  higher  organizations!  of  the  animal 
and  vegetable  world.  It  is  worthy  of  notice,  that  in  these 
theories  the  Godhead  is  attended  by  a  number  of  astral 
spirits,  who  (as  if  acquainted  with  perturbations  and  the  dis- 

explanatious  of  meteorological  processes ;  so  also  in  the  works  De  Gen- 
eralione  et  Interitu,  lib.  ii.,  cap.  3,  p.  330 ;  in  the  Meteorologicis,  lib.  i., 
cap.  12,  and  lib.  iii.,  cap.  3,  p.  372,  and  in  the  Problems  (lib.  xiv.,  cap. 
3,  lib.  viii.,  No.  9,  p.  888,  and  lib.  xiv.,  No.  3,  p.  909),  which  are  at  all 
events  based  on  Aristotelian  principles.  In  the  ancient  polarity  hypoth- 
esis, /car*  avrnrepiaTaaiv,  similar  conditions  attract  each  other,  and  dis- 
similar ones  (-J-  and  — )  repel  each  other  in  opposite  directions.  (Com 
pare  Ideler,  Meteorol.  veterum  Grcsc.  et  Rom.,  1832,  p.  10.)  The  op- 
posite  conditions,  instead  of  being  destroyed  by  combining  together, 
rather  increase  the  tension.  The  ipvxpov  increases  the  -Qeppov ;  as  in- 
versely "in  the  formation  of  hail,  the  surrounding  heat  makes  the  cold 
body  still  colder  as  the  cloud  sinks  into  warmer  strata  of  air."  Aristotle 
explains  by  his  antiperistatic  process  and  the  polarity  of  heat,  what 
modern  physics  have  taught  us  to  refer  to  conduction,  radiation,  evap- 
oration, and  changes  in  the  capacity  of  heat.  See  the  able  observations 
of  Paul  Erman  in  the  Abhandl.  tier  Berliner  Akademie  aufdasJahr  1825, 
s.  128. 

*  "  By  the  movement  of  the  heavenly  sphere,  all  that  is  unstable  in 
natural  bodies,  and  all  terrestrial  phenomena  are  produced." — Aristot., 
Mtteor.,  i.,  2,  p.  339,  and  De  Gener.  et  Corrupt.,  ii.,  10,  p.  336. 

t  Aristot.,  De  Casio,  lib.  i.,  c.  9,  p.  279  ;  lib.  ii.,  c.  3,  p.  286 ;  lib.  ii.,  c 
13,  p.  292,  Bekker.  (Compare  Biese,  bd.  i.,  s.  352-1,  357.) 

t  Aristot.,  Phys.  Auscult.,  lib.  ii.,  c.  8,  p.  199;  De  Anima,  lib.  iii.,  o 
12,  p.  434 ;  De  Animal.  General.,  lib.  v.,  c.  1,  p.  778,  Bekker. 


16  COSMOS. 

tribution  of  masses)  maintain  the  planets  in  their  eternal  oib- 
its.*  The  stars  here  reveal  the  image  of  the  divinity  in  the 
visible  world.  We  do  not  here  refer,  as  its  title  might  lead 
to  suppose,  to  the  little  pseudo- Aristotelian  work  entitled  the 
"  Cosmos,"  undoubtedly  a  Stoic  production.  Although  it  de- 
scribes the  heavens  and  the  earth,  and  oceanic  and  aerial 
currents,  with  much  truthfulness,  and  frequently  with  rhetor- 
ical animation  and  picturesque  coloring,  it  shows  no  tenden- 
cy to  refer  cosmical  phenomena  to  general  physical  princi- 
ples based  on  the  properties  of  matter. 

I  have  purposely  dwelt  at  length  on  the  most  brilliant  pe- 
riod of  the  Cosmical  views  of  antiquity,  in  order  to  contrast 
the  earliest  efforts  made  toward  the  generalization  of  ideas 
with  the  efforts  of  modern  times.  In  the  intellectual  move- 
ment of  centuries,  whose  influence  on  the  extension  of  cos- 
mical contemplation  has  been  defined  in  another  portion  of 
the  present  work.f  the  close  of  the  thirteenth  and  the  begin- 
ning of  the  fourteenth  century  were  specially  distinguished  ; 
but  the  Opus  Majus  of  Roger  Bacon,  the  Mirror  of  Nature 
of  Vincenzo  de  Beauvais,  the  Physical  Geography  (Liber  Cos- 
mographictis)  of  Albertus  Magnus,  the  Picture  of  the  World 
(Imago  Mundi)  of  Cardinal  Petrus  d'Alliaco  (Pierre  d'Ailly), 
are  works  which,  however  powerfully  they  may  have  influ- 
enced the  age  in  which  they  were  written,  do  not  fulfill  by 
their  contents  the  promise  of  their  titles.  Among  the  Italian 
opponents  of  Aristotle's  physics,  Bernardino  Telesio  of  Cosen- 
za  is  designated  the  founder  of  a  rational  science  of  nature. 
All  the  phenomena  of  inert  matter  are  considered  by  him  as 
the  effects  of  two  incorporeal  principles  (agencies  or  forces) 
—  heat  and  cold.  All  forms  of  organic  life  —  "animated" 

*  See  the  passage  in  Aristot.,  Meteor.,  xii.,  8,  p.  1074,  of  which  there 
is  a  remarkable  elucidation  in  the  Commentary  of  Alexander  Aphro- 
iisiensis.  The  stars  are  not  inanimate  bodies,  but  must  be  regarded  as 
active  and  living  beings.  (Aristot.,  De  Casio,  lib.  ii.,  cap.  12,  p.  292.) 
They  are  the  most  divine  of  created  things ;  TO.  -Qeiorepa  TUV  <j>avepuv. 
(Aristot.,  De  Casio,  lib.  i.,  cap.  9,  p.  278,  and  lib.  ii.,  cap.  1,  p.  284.) 


ip.  6,  p.  400),  me  nigh  anner  is  also  called  divine  (cap. 
That  which  the  imaginative  Kepler  calls  moving  spirits  (anima  motruai) 
in  his  work,  Mysterium  Cotmographicum  (cap.  20,  p.  71),  is  the  distort- 
ed idea  of  a  force  (virtus')  whose  main  seat  is  in  the  sun  (anima  mun- 
di),  and  which  is  decreased  by  distance  in  accordance  with  the  laws  of 
light,  and  impels  the  planets  in  elliptic  orbita.  (Compare  Apelt,  Epoch 
en  der  Gesch.  der  Mcnechheit,  bd.  i.,  e.  274.) 
*  Cotmot,  vol.  ii.,  p.  241-250. 


INTRODUCTION.  17 

plants  and  animals — are  the  effect  of  these  two  ever-divided 
forces,  of  which  the  one,  heat,  specially  appertains  to  the  ce- 
lestial, and  the  other,  cold,  to  the  terrestrial  sphere. 

"With  yet  more  unbridled  fancy,  but  with  a  profound  spirit 
of  inquiry,  Giordano  Bruno  of  Nola  attempted  to  comprehend 
the  whole  universe,  in  three  works,*  entitled  De  la  causa 
Principio  e  Uno;  Contcmplationi  circa  lo  Infinite,  Uni- 
verso  e  Atondi  innumerabili ;  and  De  Minima  et  Maximo. 
In  the  natural  philosophy  of  Telesio,  a  cotemporary  of  Co- 
pernicus, we  recognize  at  all  events  the  tendency  to  reduce 
the  changes  of  matter  to  two  of  its  fundamental  forces,  which, 
although  "  supposed  to  act  from  without,"  yet  resemble  the 
fundamental  forces  of  attraction  and  repulsion  in  the  dy- 
namic theory  of  nature  of  Boscovich  and  Kant.  The  cos- 
mical  views  of  the  Philosopher  of  Nola  are  purely  meta- 
physical, and  do  not  seek  the  causes  of  sensuous  phenomena 
in  matter  itself,  but  treat  of  "the  infinity  of  space,  filled 
with  self  -  illumined  worlds,  of  the  animated  condition  of 
those  worlds,  and  of  the  relations  of  the  highest  intelligence 
— God — to  the  universe." 

Scantily  endowed  with  mathematical  knowledge,  Giorda- 
no Bruno  continued  nevertheless  to  the  period  of  his  fearful 
martyrdomf  an  enthusiastic  admirer  of  Copernicus,  Tycho 
Brahe,  and  Kepler.  He  was  cotemporary  with  Galileo,  but 
did  not  live  to  see  the  invention  of  the  telescope  by  Hans 
Lippershey  and  Zacharias  Jansen,  and  did  not  therefore  wit- 
ness the  discovery  of  the  "  lesser  Jupiter  world,"  the  phases 
of  Venus,  and  the  nebulse.  "With  bold  confidence  in  what 
he  terms  the  lume  interno,  ragione  naturale,  altezza  dell' 
intclletto  (force  of  intellect),  he  indulged  in  happy  conjec- 
tures regarding  the  movement  of  the  fixed  stars,  the  planet 

*  Compare  the  acute  and  learned  commentary  on  the  works  of  the 
Philosopher  of  Nola,  in  the  treatise  Jordano  Bruno  par  Christian  Bar- 
tholmess,  torn,  ii.,  1847,  p.  129,  149,  and  201. 

t  He  was  burned  at  Rome  on  the  17th  of  February,  1600,  pursuant 
to  the  sentence  "  ut  qnam  clementissime  et  citra  sanguinis  effusionem 
puniretur."  Bruno  was  imprisoned  six  years  in  the  Piombi  at  Venice, 
and  two  years  in  the  Inquisition  at  Rome.  When  the  sentence  of  death 
was  announced  to  him,  Bruno,  calm  and  unmoved,  gave  utterance  to 
the  following  noble  expression:  "Majori  forsitan  cum  timore  sententi- 
am  in  me  fertis  quam  ego  accipiam."  When  a  fugitive  from  Italy  in 
1580,  he  taught  at  Geneva,  Lyons,  Toulouse,  Paris,  Oxford,  Marburg, 
Wittenberg  (which  he  calls  the  Athens  of  Germany),  Prague,  and  Helm- 
stedt,  where,  in  1589,  he  completed  the  scientific  instruction  of  Duko 
Henry  Julius  of  Brunswick- Wolfenbuttel. — Bartholmess,  torn .  i ,  p.  167- 
178.  He  also  taught  at  Padua  subsequently  to  1592. 


18  COSMOS. 

ary  nature  of  comets,  and  the  deviation  from  the  spherical 
form  observed  in  the  figure  of  the  earth.*  Greek  antiquity 
is  also  replete  with  uranological  presentiments  of  this  na- 
ture, which  were  realized  in  later  times. 

In  the  development  of  thought  on  cosmical  relations,  of 
which  the  main  forms  and  epochs  have  been  already  enu- 
merated, Kepler  approached  the  nearest  to  a  mathematical 
application  of  the  theory  of  gravitation,  more  than  seventy- 
eight  years  before  the  appearance  of  Newton's  immortal 
work,  Principia  Philosophies  Naturalis.  For  while  the 
eclectic  Simplicius  only  expressed  in  general  terms  "  that 
the  heavenly  bodies  were  sustained  from  falling  in  conse- 
quence of  the  centrifugal  force  being  superior  to  the  inher- 
ent falling  force  of  bodies  and  to  the  downward  traction  ;" 
while  Joannes  Philoponus,  a  disciple  of  Ammonius  Hermeas, 
ascribed  the  movement  of  the  celestial  bodies  to  "  a  primi- 
tive impulse,  and  the  continued  tendency  to  fall ;"  and  while, 
as  we  have  already  observed,  Copernicus  defined  only  the 
general  idea  of  gravitation,  as  it  acts  in  the  sun,  as  the  center 
of  the  planetary  world,  in  the  earth  and  in  the  moon,  using 
these  memorable  words,  "  Gravitatem  non  aliud  esse  quam 
appetentiam  quandam  naturalem  partibus  inditam  a  divina 
providentia  opificis  universorum,  ut  in  unitatem  integrita- 
temque  suam  sese  conferant,  in  formam  globi  coeuntes  ;" 
Kepler,  in  his  introduction  to  the  book  De  Stella  MartisJ 
was  the  first  who  gave  numerical  calculations  of  the  forces 
of  attraction  reciprocally  exercised  upon  each  other,  accord- 
ing to  their  relative  masses,  by  the  earth  and  moon.  He 

*  Bartholmess,  torn,  ii.,  p.  219,  232,  370.  Bruno  carefully  collected 
all  the  separate  observations  made  on  the  celestial  phenomenon  of  the 
sudden  appearance,  in  1572,  of  a  new  star  in  Cassiopeia.  Much  dis- 
cussion has  been  directed  in  modern  times  to  the  relation  existing  be- 
tween Bruno,  his  two  Calabrian  fellow-countrymen,  Bernardino  Tele- 
sio  and  Thomas  Campanella,  and  the  platonic  cardinal,  Nicolaus  Krebs 
of  Cusa.  See  Cosmos,  vol.  ii.,  p.  310,  311,  note. 

t  "  Si  duo  lapides  in  aliquo  loco  Mundi  collocarentur  propinqui  in- 
vicem,  extra  orbem  virtutis  tertii  cognati  corporis ;  illi  lapides  ad  simil- 
itudinem  duorum  Magneticorum  corporum  coirent  loco  intermedio,  qui- 
libet  accedens  ad  alterum  tanto  intervallo,  quanta  est  alterius  moles  in 
comparatione.  Si  luna  et  terra  non  retinerentur  vi  animali  (!)  aut  alia 
aliqua  aequipollente,  quselibet  in  suo  circuitu,  Terra  adscenderet  ad  Lu- 
nam  quinquagesima  quarta  parte  intervalli,  Luna  descenderet  ad  Ter- 
rarn  quinquaginta  tribus  circiter  partibus  intervalli;  ibi  jungerentur, 
posito  tamen  quod  substantia  utriusque  sit  unius  et  ejusdem  densitatis." 
—Kepler,  A&tronomia  nova,  seu  Physica  ccclestis  de  Motibus  Stella  Mar- 
tis,  1609.  Introd.,  fol.  v.  On  the  older  views  regarding  gravitation, 
see  Cosmos,  vrl.  ii.,  p.  310. 


INTRODUCTION.  19 

distinctly  adduces  the  tides  as  evidence*  that  the  attractiv& 
force  of  the  moon  (virtus  tractoria)  extends  to  the  earth , 
and  that  this  force,  similar  to  that  exerted  by  the  magnet 
on  iron,  would  deprive  the  earth  of  its  water  if  the  forme] 
should  cease  to  attract  it.  Unfortunately,  this  great  man 
was  induced,  ten  years  afterward,  in  1619,  probably  from 
deference  to  Galileo,  who  ascribed  the  ebb  and  flow  of  the 
ocean  to  the  rotation  of  the  earth,  to  renounce  his  correct 
explanation,  and  depict  the  earth  in  the  Harmonice  Mundt 
as  a  li ving  monster,  whose  whale-like  mode  of  breathing  oc- 
casioned the  rise  and  fall  of  the  ocean  in  recurring  periods 
of  sleeping  and  waking,  dependent  on  solar  time.  When  we 
remember  the  mathematical  acumen  that  pervades  one  of  the 
works  of  Kepler,  and  of  which  Laplace  has  already  made 
honorable  mention,t  it  is  to  be  lamented  that  the  discoverer 
of  the  three  great  laws  of  all  planetary  motion  should  not 
have  advanced  on  the  path  whither  he  had  been  led  by  his 
views  on  the  attraction  of  the  masses  of  cosmical  bodies. 

Descartes,  who  was  endowed  with  greater  versatility  of 
physical  knowledge  than  Kepler,  and  who  laid  the  founda- 
tion of  many  departments  of  mathematical  physics,  under- 
took to  comprise  the  whole  world  of  phenomena,  the  heav- 

*  "  Si  Terra  cessaret  attrahere  ad  se  aquas  suas,  aquae  marinse  omnes 
elevarentur  et  in  corpus  Luna?  iufluerent.  Orbis  virtutis  tractoriae,  qua? 
est  in  Luna,  porrigitur  usque  ad  terras,  et  prolectat  aquas  quacunque 
in  verticem  loci  incidit  sub  Zonam  torridam,  quippe  in  occursum  suum 
quacunque  in  verticem  loci  incidit,  insensibiliter  in  maribus  inclusis, 
sensibiliter  ibi  ubi  sunt  latissimi  alvei  Oceani  propinqui,  aquisque  spa- 
ciosa  reciprocationis  libertas."  (Kepler,  1.  c.)  "  Undas  a  Luna  trahi 
ut  ferrum  a  Magnete."  ....  Kepleri  Harmonice  Mundi,  libri  quinque, 
1619,  lib.  iv.,  cap.  7,  p.  162.  The  same  work  which  presents  us  with 
so  many  admirable  views,  among  others,  with  the  data  of  the  establish- 
ment of  the  third  law  (that  the  squares  of  the  periodic  times  of  two 
planets  are  as  the  cubes  of  their  mean  distance),  is  distorted  by  the 
wildest  flights  of  fancy  on  the  respiration,  nutrition,  and  heat  of  the 
earth-animal,  on  the  soul,  memory  (memoria  animce  Terra),  and  crea- 
tive imagination  (anima  Tdluris  imaginatio)  of  this  monster.  This  great 
man  was  so  wedded  to  these  chimeras,  that  he  warmly  contested  his 
right  of  priority  in  the  views  regarding  the  earth-animal  with  the  mys- 
tic author  of  the  Macrocosmcs,  Robert  Fludd,  of  Oxford,  who  is  report- 
ed to  have  participated  in  the  invention  of  the  thermometer.  (Harm. 
Mitndi,  p.  252.)  In  Kepler's  writings,  the  attraction  of  masses  is  often 
confounded  with  magnetic  attraction.  "  Corpus  solis  esse  magneticum. 
Virtutem,  quae  Planetas  movet,  residere  in  corpore  solis." — Stella  Mar 
tit,  pars  iii.,  cap.  32,  34.  To  each  planet  was  ascribed  a  magnetic  axis, 
which  constantly  pointed  to  one  and  the  same  quarter  of  the  heavens. 
CApelt,  Joh.  Kepler's  Astron.  Weltansicht,  1849,  8.  73. 

t  Compare  Cosmos,  vol.  ii.,  p.  327  (and  iiole 


20  COSMOS. 

enly  sphere  and  all  that  he  knew  concerning  the  animate 
and  inanimate  parts  of  terrestrial  nature,  in  a  work  entitled 
Traite  du  Monde,  and  also  Summa  Philosophies.  The  or- 
ganization of  animals,  and  especially  that  of  man — a  subject 
to  which  he  devoted  the  anatomical  studies  of  eleven  years* 
— was  to  conclude  the  work.  In  his  correspondence  with 
Father  Mersenne,  we  frequently  find  him  complaining  of  hia 
slow  progress,  and  of  the  difficulty  of  arranging  so  large  a 
mass  of  materials.  The  Cosmos  which  Descartes  always 
called  "  his  world"  (son  monde)  was  at  length  to  have  been 
sent  to  press  at  the  close  of  the  year  1633,  when  the  report 
of  the  sentence  passed  by  the  Inquisition  at  Rome  on  Gali- 
leo, which  was  first  made  generally  known  four  months  aft- 
erward, in  October,  1633,  by  Gassendi  and  Bouillaud,  at 
once  put  a  stop  to  his  plans,  and  deprived  posterity  of  a  great 
work,  completed  with  much  pains  and  infinite  care.  The 
motives  that  restrained  him  from  publishing  the  Cosmos 
were,  love  of  peaceful  retirement  in  his  secluded  abode  at 
Deventer,  and  a  pious  desire  not  to  treat  irreverentially  the 
decrees  pronounced  by  the  Holy  Chair  against  the  planetary 
movement  of  the  earth. t  In  1664,  fourteen  years  after  the 
death  of  the  philosopher,  some  fragments  were  first  printed 
under  the  singular  title  of  Le  Monde,  ou  Traite  de  la  Lu- 
miere."i.  The  three  chapters  which  treat  of  light  scarcely, 
however,  constitute  a  fourth  part  of  the  work  ;  while  those 
sections  which  originally  belonged  to  the  Cosmos  of  Des- 
cartes, and  treated  of  the  movement  of  the  planets,  and  their 
distance  from  the  sun,  of  terrestrial  magnetism,  the  ebb  and 
flow  of  the  ocean,  earthquakes,  and  volcanoes,  have  been 
transposed  to  the  third  and  fourth  portions  of  the  celebrated 
work,  Principes  de  la  Philosophic. 

Notwithstanding  its  ambitious  title,  the  Cosmotheoros  of 
Huygens,  which  did  not  appear  till  after  his  death,  scarcely 
deserves  to  be  noticed  in  this  enumeration  of  cosmological 
efforts.  It  consists  of  the  dreams  and  fancies  of  a  great  man 
on  the  animal  and  vegetable  worlds,  of  the  most  remote  cos- 
mical  bodies,  and  especially  of  the  modifications  of  form  which 

»  See  La  Vie  de  M.  Descartes  (par  Baillet),  1691,  Part  i.,  p.  197, 
End  CEuvret  de  Descartes,  publiees  par  Victor  Cousin,  torn,  i.,  1824, 
p.  101. 

t  Lsttres  de  Descartes  au  P.  Mersenne,  du,  19  Nov.,  1633,  et  du  5  Jan- 
vier, 1634.  (Baillet,  Part  i.,  p.  244-247.) 

\  The  Latin  translation  bears  the  title  Mundus  give  Dissertalio  de 
Lwmine  itt  et  de  aliis  Sensuum  Objectis  primariis.  See  Descartes,  Optu~ 
cula  posthuma  Physka  et  Mathematica,  Amst.,  1704. 


INTRODUCTION.  21 

the  human  race  may  there  present.  The  reader  might  sup- 
pose he  were  perusing  Kepler's  Somnium  Astronomicum,  or 
Kircher's  Iter  Extaticus.  As  Huygens,  like  the  astronomers 
of  our  own  day,  denied  the  presence  of  air  and  water  in  the 
moon,*  he  is  much  more  embarrassed  regarding  the  exist- 
ence of  inhabitants  in  the  moon  than  of  those  in  the  remoter 
planets,  which  he  assumes  to  be  "  surrounded  with  vapors 
and  clouds." 

The  immortal  author  of  the  Philosophic  Naturalis  Prin- 
cipia  Mathematica  (Newton)  succeeded  in  embracing  the 
whole  uranological  portion  of  the  Cosmos  in  the  causal  con- 
nection of  its  phenomena,  by  the  assumption  of  one  all-con- 
trolling fundamental  moving  force.  He  first  applied  phys- 
ical astronomy  to  solve  a  great  problem  in  mechanics,  and 
elevated  it  to  the  rank  of  a  mathematical  science.  The 
quantity  of  matter  in  every  celestial  body  gives  the  amount 
of  its  attracting  force  ;  a  force  which  acts  in  an  inverse  ra- 
tio to  the  square  of  the  distance,  and  determines  the  amount 
of  the  disturbances,  which  not  only  the  planets,  but  all  the 
bodies  in  celestial  space,  exercise  on  each  other.  But  the 
Newtonian  theory  of  gravitation,  so  worthy  of  our  admira- 
tion from  its  simplicity  and  generality,  is  not  limited  in  its 
cosmical  application  to  the  uranological  sphere,  but  com- 
prises also  telluric  phenomena,  in  directions  not  yet  fully 
investigated  ;  it  affords  the  clew  to  the  periodic  movements 
in  the  ocean  and  the  atmosphere,!  and  solves  the  problems 
of  capillarity,  of  endosmosis,  and  of  many  chemical,  elec- 

*  "  Lunam  aqnis  carere  et  afire :  Marium  similitudinem  in  Luna  nul- 
lam  reperio.  Nam  regiones  planas  quae  montosis  multo  obscuriores 
eunt,  quasque  vulgo  pro  maribus  haberi  video  et  oceanorum  nominibus 
insigniri,  in  his  ipsis,  longiore  telescopic  inspectis,  cavitates  exiguas  in- 
esse  comperio  rotundas,  umbris  intus  cadentibus;  quod  maris  superfi- 
ciei  convenire  nequit;  turn  ipsi  campi  illi  latiores  non  prorsus  eequabi- 
lem  superficiem  praDferunt,  cum  diligentius  eas  intuemur.  Quod  circa 
maria  esse  non  possunt,  sed  materia  constare  debent  minus  candicante, 
quam  qute  est  partibus  asperioribus  in  quibus  rursus  quanlam  viridiori 
lumine  caeteras  prsecellunt." — Hugenii  Cosmotheorog,  ed.  alt.  1699,  lib. 
xi.,  p.  114.  Huygens  conjectures,  however,  that  Jupiter  is  agitated  by 
much  wind  and  rain,  for  "  ventorum  flatus  ex  ilia  nubium  Jovialium 
mutabili  facie  cognoscitur"  (lib.  i.,  p.  69).  These  dreams  of  Huygens 
regarding  the  inhabitants  of  remote  planets,  so  unworthy  of  a  man  versed 
iu  exact  mathematics,  have,  unfortunately,  been  revived  by  Emauuel 
Kant,  in  his  cdmirable  work  Allgemeine  Naturgeschichte  und  Theorie 
dtt  Himmelt,  1755  (s.  173-192). 

t  See  Laplace  (des  Oscillations  de  t 'Atmotphlre,  du  flux  Solaire  et 
Lunaire}  iu  the  Micanique  Celeste,  livre  iv.,  and  in  the  Exposition  d* 
Syst.  du  Monde,  1824,  p.  291-296. 


22  COSMOS. 

tro-magnetic,  and  organic  processes.  Newton*  even  distin- 
guished the  attraction  of  masses ,  as  manifested  in  the  mo- 
tion of  cosmical  bodies  and  in  the  phenomena  of  the  tides, 
from  molecular  attraction,  which  acts  at  infinitely  small 
distances  and  in  the  closest  contact. 

Thus  we  see  that  among  the  various  attempts  which  have 
been  made  to  refer  whatever  is  unstable  in  the  sensuous 
world  to  a  single  fundamental  principle,  the  theory  of  grav- 
itation is  the  most  comprehensive  and  the  richest  in  cosmic- 
al results.  It  is  indeed  true,  that  notwithstanding  the  brill- 
iant progress  that  has  been  made  in  recent  times  in  strechi- 
ometry  (the  art  of  calculating  with  chemical  elements  and 
in  the  relations  of  volume  of  mixed  gases),  all  the  physical 
theories  of  matter  have  not  yet  been  referred  to  mathematic- 
ally-determinable  principles  of  explanation.  Empirical  laws 
have  been  recognized,  and  by  means  of  the  extensively- dif- 
fused views  of  the  atomic  or  corpuscular  philosophy,  many 
points  have  been  rendered  more  accessible  to  mathematical 
investigation ;  but,  owing  to  the  unbounded  heterogeneous- 
ness  of  matter  and  the  manifold  conditions  of  aggregation  of 
particles,  the  proofs  of  these  empirical  laws  can  not  as  yet 
by  any  means  be  developed  from  the  theory  of  contact-at- 
traction with  that  certainty  which  characterizes  the  estab- 
lishment of  Kepler's  three  great  empirical  laws  derived  from 
the  theory  of  the  attraction  of  masses  or  gravitation. 

At  the  time,  however,  that  Newton  recognized  all  move- 
ments of  the  cosmical  bodies  to  be  the  results  of  one  and  the 
same  force,  he  did  not,  like  Kant,  regard  gravitation  as  an 
essential  property  of  bodies,!  but  considered  it  either  as  the 

*  Adjicere  jam  licet  de  spiritu  quodam  subtilissimo  corpora  crassa 
pervadente  et  in  iisdem  latente,  cujus  vi  et  actiouibus  particulaj  corpo- 
rum  ad  minimas  distantias  se  mutuo  attrahunt  et  contiguae  facta  cohac- 
rent. — Newton,  Principia  Phil.  Nat.  (ed.  Le  Sueur  et  Jacquier,  1760), 
Schol.  gen.,  t.  iii.,  p.  676;  compare  also  Newton's  Optics  (ed.  1718), 
Query  31,  p.  305,  353,  367,  372.  (Laplace,  Syst.  du  Monde,  p.  384,  and 
Cosmos,  vol.  i.,  p.  63  (note).) 

t  Hactenus  phaenomena  coelorum  et  maris  nostri  per  vim  gravitatis 
exposui,  sed  causam  gravitatis  nondum  assignavi.  Oritur  utique  haec 
vis  a  causa  aliqua,  qua:  penetrat  ad  usque  centra  solis  et  planetarum, 
sine  virtutis  dimiuutione ;  quaeque  agit  non  pro  quantitate  superficierum 
particularum,  in  quas  agit  (ut  solent  causae  mechanics),  sed  pro  quanti- 
tate materiae  solidao. — Rationem  harum  gravitatis  proprietatum  ex  phae- 
nomenis  nondum  potui  deducere  et  hypotheses  non  fingo.  Satis  est 
quod  gravitas  revera  existat  et  agat  secundum  leges  a  nobis  expositas. 
— Newton,  Principia  Phil.  Nat.,  p.  676.  "  To  tell  us  that  every  spe- 
cies of  things  is  endowed  witlr.  an  occult  specific  quality,  by  which  it 
acts  and  produces  manifest  effects,  is  to  tell  us  nothing ;  but  to  derive 


INTRODUCTION.  23 

result  of  some  higher  and  still  unknown  power,  or  of  "  the 
centrifugal  force  of  the  aether,  which  fills  the  realms  of  space, 
and  is  rarer  within  bodies,  but  increases  in  density  outward. 
The  latter  view  is  set  forth  in  detail  in  a  letter  to  Robert 
Boyle*  (dated  February  28,  1678),  which  ends  with  the 
words,  "  I  seek  the  cause  of  gravity  in  the  sether."  Eight 
years  afterward,  as  we  learn  from  a  letter  he  wrote  to  Hal 
ley,  Newton  entirely  relinquished  this  hypothesis  of  the  rarer 
and  denser  sether.f  It  is  especially  worthy  of  notice,  that 
in  1717,  nine  years  before  his  death,  he  should  have  deemed 
it  necessary  expressly  to  state,  in  the  short  preface  to  the  sec- 
ond edition  of  his  Optics,  that  he  did  not  by  any  means  con- 
sider gravity  as  an  "  essential  property  of  bodies  ;"J  while 

two  or  three  general  principles  of  motion  from  phenomena,  and  after- 
ward to  tell  us  how  the  properties  and  actions  of  all  corporeal  things 
follow  from  those  manifest  principles,  would  be  a  very  great  step  in  phi- 
losophy, though  the  causes  of  those  principles  were  not  yet  discovered ; 
and  therefore  I  scruple  not  to  propose  the  principles  of  motion,  and  leave 
their  causes  to  be  found  out." — Newton's  Optics,  p.  377.  In  a  previ- 
ous portion  of  the  same  work,  at  query  31,  p.  351,  he  writes  as  follows : 
"  Bodies  act  one  upon  another  by  the  attraction  of  gravity,  magnetism, 
and  electricity ;  and  it  is  not  improbable  that  there  may  be  more  at- 
tractive powers  than  these.  How  these  attractions  may  be  performed 
I  do  not  here  consider.  What  I  call  attraction  may  be  performed  by 
impulse,  or  by  some  other  means  unknown  to  me.  I  use  that  word 
lio  <;  to  signify  only  in  general  any  force  by  which  bodies  tend  toward 
on^  another,  whatsoever  be  the  cause." 

*  "  I  suppose  the  rarer  sether  within  bodies,  and  the  denser  without 
them." — Operum  Newtoni,  tomus  iv.  (ed.  1782,  Sam.  Horsley),  p.  386. 
The  above  observation  was  made  in  reference  to  the  explanation  of  the 
discovery  made  by  Grimaldi  of  the  diffraction  or  inflection  of  light.  At 
the  close  of  Newton's  letter  to  Robert  Boyle,  February,  1678,  p.  94,  he 
says :  "  I  shall  set  down  one  conjecture  more  which  came  into  my  mind: 
it  is  about  the  cause  of  gravity.  .  .  ."  His  correspondence  with  Olden- 
burg (December,  1675)  shows  that  the  great  philosopher  was  not  at 
that  time  averse  to  the  "  aether  hypotheses."  According  to  these  views, 
the  impulse  of  material  light  causes  the  aether  to  vibrate ;  but  the  vibra- 
tions of  the  sether  alone,  which  fias  some  affinity  to  a  nervous  fluid,  does 
not  generate  light.  In  reference  to  the  contest  with  Hooke,  consult 
Horsley,  t.  iv.,  p.  378-380. 

t  See  Brewster's  Life  of  Sir  Isaac  Newton,  p.  303-305. 

t  Newton's  words  "  not  to  take  gravity  for  an  essential  property  of 
bodies"  in  the  "  Second  Advertisement"  contrast  with  his  remarks  on 
the  forces  of  attraction  and  repulsion,  which  he  ascribes  to  all  molecu- 
lar particles,  in  order,  according  to  the  theory  of  emission,  to  explain 
the  phenomena  of  the  refraction  and  repulsion  of  the  rays  of  light  from 
reflecting  surfaces  "without  their  actual  contact."  (Newton,  Optict, 
book  ii.,  prop.  8,  p.  241,  and  Brewster,  Op.  cit.,  p.  301.)  According 
to  Kant  (see  Die  Metaphysischen  Anfangsgrunde  der  Naturwissenschaft, 
1800,  s.  28),  we  can  not  conceive  the  existence  of  matter  without  these 
forces  of  attraction  and  repulsion.  All  physical  phenomena  are  there- 


24  COSMOS. 

Gilbert,  as  early  as  1600,  regarded  magnetism  as  a  force  in- 
herent in  all  matter.  So  undetermined  was  even  Newton, 
the  profound  and  experienced  thinker,  regarding  the  "  ulti- 
mate mechanical  cause"  of  all  motion. 

It  is  indeed  a  brilliant  effort,  worthy  of  the  human  mind, 
to  comprise,  in  one  organic  whole,  the  entire  science  of  na- 
ture from  the  laws  of  gravity  to  the  formative  impulse  (ni- 
sus  formativus)  in  animated  bodies  ;  but  the  present  imper- 
fect state  of  many  branches  of  physical  science  offers  innu- 
merable difficulties  to  the  solution  of  such  a  problem.  The 
imperfectibility  of  all  empirical  science,  and  the  boundless- 
ness of  the  sphere  of  observation,  render  the  task  of  explain- 
ing the  forces  of  matter  by  that  which  is  variable  in  matter, 
an  impracticable  one.  What  has  been  already  perceived  by 
no  means  exhausts  that  which  is  perceptible.  If,  simply  re- 
ferring to  the  progress  of  science  in  modern  times,  we  com- 
pare the  imperfect  physical  knowledge  of  Gilbert,  Robert 
Boyle,  and  Hales,  with  that  of  the  present  day,  and  remem- 
ber that  every  few  years  are  characterized  by  an  increasing 
rapidity  of  advance,  we  shall  be  better  able  to  imagine  the 
periodical  and  endless  changes  which  all  physical  sciences 
are  destined  to  undergo.  New  substances  and  new  forces 
will  be  discovered. 

Although  many  physical  processes,  as  those  of  light,  heat, 
and  electro-magnetism,  have  been  rendered  accessible  to  a 
mathematical  investigation  by  being  reduced  to  motion  or  vi- 
brations, we  are  still  without  a  solution  to  those  often  mooted 
and  perhaps  insolvable  problems  :  the  cause  of  chemical  dif- 
ferences of  matter  ;  the  apparently  irregular  distribution  of 
the  planets  in  reference  to  their  size,  density,  the  inclination 
of  their  axes,  the  eccentricity  of  their  orbits,  and  the  num- 

fore  reduced  by  him,  as  previously  by  Goodwin  Knight  (Pkilos.  Trant- 
act.  1748,  p.  264),  to  the  conflict  of  two  elementary  forces.  In  the  at- 
omic theories,  which  were  diametrically  opposed  to  Kant's  dynamic 
views,  the  force  of  attraction  was  referred,  in  accordance  with  a  view 
specially  promulgated  by  Lavoisier,  to  the  discrete  solid  elementary 
molecules  of  which  all  bodies  are  supposed  to  consist ;  while  the  force 
of  repulsion  was  attributed  to  the  atmospheres  of  heat  surrounding  all 
elementary  corpuscles.  This  hypothesis,  which  regards  the  so-called 
taloric  as  a  constantly  expanded  matter,  assumes  the  existence  of  two 
elementary  substances,  as  in  the  mythical  idea  of  two  kinds  of  tether. 
(Newton,  Optics,  query  28,  p.  339.)  Here  the  question  arises,  What 
causes  this  caloric  matter  to  expand?  Considerations  on  the  density 
of  molecules  in  comparison  with  that  of  their  aggregates  (the  entire 
body)  lead,  according  to  atomic  hypotheses,  to  the  result,  that  the  dis- 
tance between  elementary  corpuscles  is  i'ar  greater  than,  their  diameterg. 


INTRODUCTION.  25 

her  and  distance  of  their  satellites  ;  the  configuration  of  con- 
tinents, and  the  position  of  their  highest  mountain  chains. 
Those  relations  in  space,  which  we  have  referred  to  merely 
by  way  of  illustration,  can  at  present  be  regarded  only  as 
something  existing  in  nature,  as  a  fact,  but  which  I  can  net 
designate  as  merely  causal,  because  their  causes  and  mutual 
connection  have  not  yet  been  discovered.  They  are  the  re- 
sult of  occurrences  in  the  realms  of  space  coeval  with  the 
formation  of  our  planetary  system,  and  of  geognostic  process- 
es in  the  upheaval  of  the  outer  strata  of  the  earth  into  con- 
tinents and  mountain  chains.  Our  knowledge  of  the  prime- 
val ages  of  the  world's  physical  history  does  not  extend  suf- 
ficiently far  to  allow  of  our  depicting  the  present  condition 
of  things  as  one  of  development.* 

Wherever  the  causal  connection  between  phenomena  has 
not  yet  been  fully  recognized,  the  doctrine  of  the  Cosmos,  or 
the  physical  description  of  the  universe,  does  not  constitute  a 
distinct  branch  of  physical  science.  It  rather  embraces  the 
whole  domain  of  nature,  the  phenomena  of  both  the  celestial 
and  terrestrial  spheres,  but  embraces  it  only  under  the  single 
point  of  view  of  efforts  made  toward  the  knowledge  of  the 
universe  as  a  whole. "f  As,  in  the  "  exposition  of  past  events 
in  the  moral  and  political  world,  the  historian:):  can  only  di- 
vine the  plan  of  the  government  of  the  world,  according  to 
human  views,  through  the  signs  which  are  presented  to  him, 
and  not  by  direct  insight,"  so  also  the  inquirer  into  nature, 
in  his  investigation  of  cosmical  relations,  feels  himself  pene- 
trated by  a  profound  consciousness  that  the  fruits  hitherto 
yielded  by  direct  observation  and  by  the  careful  analysis  of 
phenomena  are  far  from  having  exhausted  the  number  of 
impelling,  producing,  and  formative  forces. 

*   Cosmos,  vol.  i.,  p.  94-97.  t  Op.  cit.,  p.  55-62. 

t  Wilhelra  von  Humboldt,  Gesammdte  Werke,  bd.  i.,  s.  23. 

VOL.  III.— B 


RESULTS  OF  OBSERVATIONS  IN  THE  URANOLOGICAL  POR- 
TION OF  THE  PHYSICAL  DESCRIPTION  OF  THE  WORLD. 

WE  again  commence  with,  the  depths  of  cosmical  space, 
and  the  remote  sporadic  starry  systems,  which  appear  to  tel- 
escopic vision  as  faintly  shining  nebulce.  From  these  we 
gradually  descend  to  the  double  stars,  revolving  round  one 
common  center  of  gravity,  and  which  are  frequently  bicol- 
ored,  to  the  nearer  starry  strata,  one  of  which  appears  to  in- 
close our  own  planetary  system ;  passing  thence  to  the  air- 
and-ocean-girt  terrestrial  spheroid  which  we  inhabit.  We 
have  already  indicated,  in  the  introduction  to  the  General 
Delineation  of  Nature,*  that  this  arrangement  of  ideas  is 
alone  suited  to  the  character  of  a  work  on  the  Cosmos,  since 
we  can  not  here,  in  accordance  with  the  requirements  of  di- 
rect sensuous  contemplation,  begin  with  our  own  terrestrial 
abode,  whose  surface  is  animated  by  organic  forces,  and  pass 
from  the  apparent  to  the  true  movements  of  cosmical  bodies. 

The  uranological,  when  opposed  to  the  telluric  domain 
of  the  Cosmos,  may  be  conveniently  separated  into  two  di- 
visions, one  of  which  comprises  astro^nosy,  or  the  region  of 
the  fixed  stars,  and  the  other  our  solar  and  planetary  sys- 
tem. It  is  unnecessary  here  to  describe  the  imperfect  and 
unsatisfactory  nature  of  such  a  nomenclature  and  such  class- 
ifications. Names  were  introduced  into  the  physical  sci- 
ences before  the  differences  of  objects  and  their  strict  limita- 
tions were  sufficiently  known.f  The  most  important  point, 
however,  is  the  connection  of  ideas,  and  the  order  in  which 
the  objects  are  to  be  considered.  Innovations  in  the  no- 
menclature of  groups,  and  a  deviation  from  the  meanings 
hitherto  attached  to  well-known  names,  only  tend  to  dis- 
tract and  confuse  the  mind. 

a.  ASTROGNOSY.     (THE  DOMAIN  OF  THE  FIXED  STARS.) 
Nothing   is  stationary  in  space.     Even  the  fixed  stars 
move,  as  Halleyl:  endeavored  to  show  in  reference  to  Sirius, 

*  Cosmos,  vol.  i.,  p.  79-83.  f  Op.  cit.,  p.  56,  57 

t  Halley,  in  the  Philos.  Transact,  for  1717,  vol.  xxx.,  p.  736. 


A8TROGNOSY.  27 

Arcturus,  and  Aldebaran,  and  as  in  modern  times  has  been 
incontrovertibly  proved  with  respect  to  many  others.  The 
bright  star  Arcturus  has,  during  the  2100  years  (since  the 
times  of  Aristi.'lus  and  Hipparchus)  that  it  has  been  ob- 
served, changed  its  position  in  relation  to  the  neighboring 
fainter  stars  2£  times  the  moon's  diameter.  Encke  remarks 
"  that  the  star  \i  Cassiopeise  appears  to  have  moved  31  lunar 
diameters,  and  61  Cygni  about  6  lunar  diameters,  if  the  an- 
cient observations  correctly  indicated  its  position."  Conclu- 
sions based  on  analogy  justify  us  in  believing  that  there  is 
every  where  progressive,  and  perhaps  also  rotatory  motion. 
The  term  "  fixed  stars"  leads  to  erroneous  preconceptions ; 
it  may  have  referred,  in  its  earliest  meaning  among  the 
Greeks,  to  the  idea  of  the  stars  being  riveted  into  the  crys- 
tal vault  of  heaven  ;  or,  subsequently,  in  accordance  with 
the  Roman  interpretation,  it  may  indicate  fixity  or  immo- 
bility. The  one  idea  involuntarily  led  to  the  other.  In  Gre- 
cian antiquity,  in  an  age  at  least  as  remote  as  that  of  Anax- 
imenes  of  the  Ionic  school,  or  of  Alcmseon  the  Pythagorean, 
all  stars  were  divided  into  wandering  (darpa  TrAavcjjueva  or 
TrAavT/rd)  and  non-wandering  fixed  stars  (drr^avelg  aarepeg 
or  dTrXavfj  darpa).*  Besides  this  generally  adopted  desig- 
nation of  the  fixed  stars,  which  Macrobius,  in  his  Somnium 
Scipionis,  Latinized  by  Sphcera  aplanesj  we  frequently 
meet  in  Aristotle  (as  if  he  wished  to  introduce  a  new  tech- 
nical term)  with  the  phrase  riveted  stars,  Ivdedeneva  darpa, 
instead  of  a^Xavr],%  as  a  designation  for  fixed  stars.  From 
this  form  of  speech  arose  the  expressions  of  sidera  infixa 
cado  of  Cicero,  Stellas  quas  ^nctamus  affixas  of  Pliny,  and  as- 

9  Pseudo-Plut.,  De  plac.  Philos.,  ii.,  15,  16 ;  Stob.,  Eclog.  Phys.,  p. 
582 ;  Plato,  in  the  Timeeus,  p.  40. 

t  Macrob.,  Sown.  Scip.,  i.,  9-10 ;  slellce  inerrantes,  in  Cicero,  De  Nat. 
Deorum,  iii.,  20. 

t  The  principal  passage  in  which  we  meet  with  the  technical  expres- 
sion hdedspeva  uarpa,  is  in  Aristot.,  De  Caelo,  ii.,  8,  p.  289, 1.  34,  p.  290, 
1.  19,  Bekker.  This  altered  nomenclature  forcibly  attracted  my  atten- 
tion in  my  investigations  into  the  optics  of  Ptolemy,  and  his  experi- 
ments on  refraction.  Professor  Franz,  to  whose  philological  acquire- 
ments  I  am  indebted  for  frequent  aid,  reminds  me  that  Ptolemy  (Syn- 
tax, vii.,  1)  speaks  of  the  fixed  stars  as  affixed  or  riveted;  uanep  Trpo- 
OTreQvKOTee.  Ptolemy  thus  objects  to  the  expression  a<j>aipa  air'Xavfjc 
(orltig  inerrans)  ;  "  in  as  far  as  the  stars  constantly  preserve  their  rela 
live  distances,  they  might  rightly  be  termed  airhavtiq ;  but  in  as  far  an 
the  sphere  in  which  they  complete  their  course,  and  in  which  they  seem 
to  have  grown,  as  it  were,  has  an  independent  motion,  the  designation 
O7r/laf!?f  is  inappropriate  if  applied  to  the  sphere." 


tra  fixa  of  Manilius,  which  corresponds  with  our  term  fixed 
stars.*  This  idea  of  fixity  leads  to  the  secondary  idea  of 
immobility,  of  persistence  in  one  spot,  and  thus  the  original 
signification  of  the  expressions  infixum  or  affixum  sidus  was 
gradually  lost  sight  of  in  the  Latin  translations  of  the  Mid- 
dle Ages,  and  the  idea  of  immobility  alone  retained.  This 
is  already  apparent  in  a  highly  rhetorical  passage  of  Seneca, 
regarding  the  possibility  of  discovering  new  planets,  in  which 
he  says  (Nat.  Queest.,  vii.,  24),  "  Credis  autem  in  hoc  max- 
imo  et  pulcherrimo  corpore  inter  innumerabiles  Stellas,  quae 
noctem  decore  vario  distinguunt,  quse  ae'ra  minime  vacuum 
et  inertem  esse  patiuntur,  quinque  solas  esse,  quibus  exer- 
cere  se  liceat ;  ceteras  stare  fixum  et  immobilempopulum?" 
"And  dost  thou  believe  that  in  this  so  great  and  splendid 
body,  among  innumerable  stars,  which  by  their  various  beau- 
ty adorn  the  night,  not  suffering  the  air  to  remain  void  and 
unprofitable,  that  there  should  be  only  five  stars  to  whom  it 
is  permitted  to  be  in  motion,  while  all  the  rest  remain  a  fixed 
and  immovable  multitude  ?"  This  fixed  and  immovable  mul- 
titude is  nowhere  to  be  found. 

In  order  the  better  to  classify  the  main  results  of  actual 
observations,  and  the  conclusions  or  conjectures  to  which 
they  give  rise,  in  the  description  of  the  universe,  I  will  sep- 
arate the  astrognostic  sphere  into  the  following  sections : 

I.  The  considerations  on  the  realms  of  space  and  the  bodies 
by  which  they  appear  to  be  filled. 

II.  Natural  and  telescopic  vision,  the  scintillation  of  the 
stars,  the  velocity  of  light,  and  the  photometric  experiments 
on  the  intensity  of  stellar  light. 

III.  The  number,  distribution,  and  color  of  the  stars ;  the 
stellar  swarms,  and  the  Milky  Way,  which  is  interspersed 
with  a  few  nebulae. 

IV.  The  newly-appeared  and  periodically-changing  stars, 
and  those  that  have  disappeared. 

V.  The  proper  motion  of  the  fixed  stars ;  the  problematical 
existence  of  dark  cosmical  bodies ;  the  parallax  and  meas- 
ured distance  of  some  of  the  fixed  stars. 

VI.  The  double  stars,  and  the  period  of  their  revolution 
round  a  common  center  of  gravity. 

VII.  The  nebulas  which  are  interspersed  in  the  Magellanic 
clouds  with  numerous  stellar  masses,  the  black  spots  (coal 
bags)  in  the  vault  of  heaven. 

*  Cicero,  De  Nat  Deorutn,  i.,  13 ;  Plin.,  ii.,  6  and  24 ;  Manillas,  ii.,  35 


THE  REALMS  OF  SPACE,  AND  CONJECTURES  REGARDING  THAT  WHICH 
APPEARS  TO  OCCUPY  THE  SPACE  INTERVENING  BETWEEN  THE 
HEAVENLY  BODIES. 

THAT  portion  of  the  physical  description  of  the  universe 
which  treats  of  what  occupies  the  distant  regions  of  the 
heavens,  filling  the  space  between  the  globular  cosmic  al 
bodies,  and  is  imperceptible  to  our  organs,  may  not  unaptly 
be  compared  to  the  mythical  commencement  of  ancient  his- 
tory. In  infinity  of  space  as  well  as  in  eternity  of  time,  all 
things  are  shrouded  in  an  uncertain  and  frequently  deceptive 
twilight.  The  imagination  is  here  doubly  impelled  to  draw 
from  its  own  fullness,  and  to  give  outline  and  permanence  to 
these  indefinite  changing  forms.*  This  observation  will,  I 
trust,  suffice  to  exonerate  me  from  the  reproach  of  confound- 
ing that  which  has  been  reduced  to  mathematical  certainty 
by  direct  observation  or  measurement,  with  that  which  is 
founded  on  very  imperfect  induction.  Wild  reveries  belong 
to  the  romance  of  physical  astronomy  ;  yet  the  mind  famil- 
iar with  scientific  labors  delights  in  dwelling  on  subjects 
such  as  these,  which,  intimately  connected  with  the  present 
condition  of  science,  and  with  the  hopes  which  it  inspires, 
have  not  been  deemed  unworthy  of  the  earnest  attention  of 
the  most  distinguished  astronomers  of  our  day. 

By  the  influence  of  gravitation,  or  general  gravity,  as  well 
as  by  light  and  radiating  heat,t  we  are  brought  in  contact,  as 
we  may  with  great  probability  assume,  not  only  with  our  own 
Sun,  but  also  with  all  the  other  luminous  suns  of  the  firma- 
ment. The  important  discovery  of  the  appreciable  resist- 
ance which  a  fluid  filling  the  realms  of  space  is  capable  of 
opposing  to  a  comet  having  a  period  of  revolution  of  five 
years,  has  been  perfectly  confirmed  by  the  exact  accordance 
of  numerical  relations.  Conclusions  based  upon  analogies 
may  fill  up  a  portion  of  the  vast  chasm  which  separates  the 
certain  results  of  a  mathematical  natural  philosophy  from 
conjectures  verging  on  the  extreme,  and  therefore  obscure 
and  barren  confines  of  all  scientific  development  of  mind. 

From  the  infinity  of  space — an  infinity,  however,  doubted 

*  Cosmos,  vol.  i.,  p.  87.     (Compare  the  admirable  observations  of 
Encke,  Ueber  die  Anordnung  des  Sternsystems,  1844,  s.  7.) 
t  Cotmot,  vol.  i.,  p.  154,  155. 


30  COSMOS. 

by  Aristotle* — follows  the  idea  of  its  immeasurability.  Sep  • 
arate  portions  only  have  been  rendered  accessible  to  meas- 
urement, and  the  numerical  results,  which  far  exceed  the 
grasp  of  our  comprehension,  become  a  source  of  mere  puerile 
gratification  to  those  who  delight  in  high  numbers,  and  im- 
agine that  the  sublimity  of  astronomical  studies  may  be 
heightened  by  astounding  and  terrific  images  of  physical  mag- 
nitude. The  distance  of  61  Cygni  from  the  Sun  is  657,000 
semi-diameters  of  the  Earth's  orbit ;  a  distance  which  light 
takes  rather  more  than  ten  years  to  traverse,  while  it  passes 
from  the  Sun  to  the  Earth  in  8'  17"-78.  Sir  John  Herschel 
conjectures,  from  his  ingenious  combination  of  photometric 
calculations,!  that  if  the  stars  in  the  great  circle  of  the  Milky 
Way  which  he  saw  in  the  field  of  his  twenty-feet  telescope 
were  newly-arisen  luminous  cosmical  bodies,  they  would  have 
required  2000  years  to  transmit  to  us  the  first  ray  of  light 
All  attempts  to  present  such  numerical  relations  fail,  either 
from  the  immensity  of  the  unit  by  which  they  must  be  meas- 
ured, or  from  the  high  number  yielded  by  the  repetition  of 
this  unit.  Bessel$  very  truly  observes  that  "  the  distance 
which  light  traverses  in  a  year  is  not  more  appreciable  to 
us  than  the  distance  which  it  traverses  in  ten  years.  There- 
fore every  endeavor  must  fail  to  convey  to  the  mind  any 
idea  of  a  magnitude  exceeding  those  that  are  accessible  on 
the  earth."  This  overpowering  force  of  numbers  is  as  clear- 
ly manifested  in  the  smallest  organisms  of  animal  life  as  in 
the  milky  way  of  those  self-luminous  suns  which  we  call 
fixed  stars.  What  masses  of  Polythalami®  are  inclosed,  ac- 
cording to  Ehrenberg,  in  one  thin  stratum  of  chalk !  This 
eminent  investigator  of  nature  asserts  that  one  cubic  inch  of 
the  Bilin  polishing  slate,  which  constitutes  a  sort  of  mount- 
ain cap  forty  feet  in  height,  contains  41,000  millions  of  the 
microscopic  Galionella  distans  ;  while  the  same  volume  con- 
tains more  than  1  billion  750,000  millions  of  distinct  indi- 
viduals of  Galionella  ferruginea.k  Such  estimates  remind 
us  of  the  treatise  named  Arenarius  (tpafifiirrj^)  of  Archime- 
des— of  the  sand-grains  which  might  fill  the  universe  of 
space  !  If  the  starry  heavens,  by  incalculable  numbers, 
magnitude,  space,  duration,  and  length  of  periods,  impress 

*  Aristot.,  De  Casio,  1,  7,  p.  276,  Bekker. 

t  Sir  John  Herschel,  Outlines  of  Astronomy,  1849,  §  803,  p.  541. 
j  Bessel,  in  Schumacher's  Jahrluchfur  1839,  s.  50. 
$  Ehrenberg,  Abhandl.  der  Berl.  Akad.,  1838,  s.  59 ;  also  in  his  Info 
rionsthiere,  B.  170. 


THE    PROPAGATION    OP   LIGHT.  31 

man  with  the  conviction  of  his  own  insignificance,  his  phys- 
ical weakness,  and  the  ephemeral  nature  of  his  existence ; 
he  is,  on  the  other  hand,  cheered  and  invigorated  by  the 
consciousness  of  having  been  enabled,  by  the  application  and 
development  of  intellect,  to  investigate  very  many  important 
points  in  reference  to  the  laws  of  Nature  and  the  sidereal 
arrangement  of  the  universe. 

Although  not  only  the  propagation  of  light,  but  also  a 
special  form  of  its  diminished  intensity,  the  resisting  medium 
acting  on  the  periods  of  revolution  of  Encke's  comet,  and  the 
evaporation  of  many  of  the  large  tails  of  comets,  seem  to 
prove  that  the  regions  of  space  which  separate  cosmical  bod- 
ies are  not  void,*  but  filled  with  some  kind  of  matter ;  we 
must  not  omit  to  draw  attention  to  the  fact  that,  among  the 
now  current  but  indefinite  expressions  of  "  the  air  of  Jieav- 
en"  "  cosmical  (non-luminous)  matter"  and  "  ether"  the 
latter,  which  has  been  transmitted  to  us  from  the  earliest  an- 
tiquity of  Southern  and  Western  Asia,  has  not  always  ex- 
pressed the  same  idea.  Among  the  natural  philosophers  of 
India,  ether  (aka'sa)  was  regarded  as  belonging  to  the  pant- 
scJiata,  or  five  elements,  and  was  supposed  to  be  a  fluid  of 
infinite  subtlety,  pervading  the  whole  universe,  and  constitu- 
ting the  medium  of  exciting  life  as  well  as  of  propagating 
sound.f  Etymologically  considered,  aka'sa  signifies,  accord- 
ing to  Bopp,  "  luminous  or  shining,  and  bears,  therefore,  in 
its  fundamental  signification,  the  same  relation  to  the  '  ether' 
of  the  Greeks  as  shining  does  to  burning." 

In  the  dogmas  of  the  Ionic  philosophy  of  Anaxagoras  and 
Empedocles,  this  ether  (alOr^p)  differed  wholly  from  the  act- 
ual (denser)  vapor-charged  air  (drjp)  which  surrounds  the 

*  Aristotle  (Phys.  Auseu.lt.,  iv.,  6-10,  p.  213-217,  Bekker)  proves,  in 
opposition  to  Leucippus  and  Democritus,  that  there  is  no  unfilled  space 
— no  vacuum  in  the  universe. 

t  Akd'sa  signifies,  according  to  Wilson's  Sanscrit  Dictionary,  "  the 
subtle  and  ethereal  fluid  supposed  to  fill  and  pervade  the  universe,  and 
to  be  the  peculiar  vehicle  of  life  and  sound."  "  The  word  dlcd'sa  (lu- 
minous, shining)  is  derived  from  the  root  ka's  (to  shine),  to  which  is 
added  the  preposition  d.  The  quintuple  of  all  the  elements  is  called 
•pantsckatd,  or  pantschatra,  and  the  dead  are,  singularly  enough,  desig- 
nated as  those  who  have  been  resolved  into  the  five  elements  (prdpta 
pantschatra').  Such  is  the  interpretation  given  in  the  text  of  Amara- 
koscha,  Amarasinha's  Dictionary." — (Bopp.)  Colebrooke's  admirable 
treatise  on  the  Sankhya  Philosophy  treats  of  these  five  elements ;  see 
Transact,  of  the  Asiat.  Soc.,  vol.  i.,  Loud.,  1827,  p.  31.  Strabo  refers, 
according  to  Megasthenes  (xv.,  $  59,  p.  713,  Gas.),  to  the  all-forming 
fifth  element  of  the  Indians,  without,  however,  naming  it. 


32  COSMOS. 

earth,  and  "  probably  extends  as  far  as  the  moon."  It  was 
of  "  a  fiery  nature,  a  brightly-beaming,  pure  fire-air,*  of  great 
subtlety  and  eternal  serenity."  This  definition  perfectly  co- 
incides with  its  etymological  derivation  from  aWeiv,  to  burn, 
for  which  Plato  and  Aristotle,  from  a  predilection  for  me- 
chanical views,  singularly  enough  substituted  another  (del- 
6elv),  on  account  of  the  constancy  of  the  revolving  and  rota- 
tory movement.!  The  idea  of  the  subtlety  and  tenuity  of 
the  upper  ether  does  not  appear  to  have  resulted  from  a 
knowledge  that  the  air  on  mountains  is  purer  and  less 
charged  with  the  heavy  vapors  of  the  earth,  or  that  the  dens- 
ity of  the  strata  of  air  decreases  with  their  increased  height. 
In  as  far  as  the  elements  of  the  ancients  refer  less  to  mate- 
rial differences  of  bodies,  or  even  to  their  simple  nature  (their 
incapacity  of  being  decomposed),  than  to  mere  conditions  of 
matter,  the  idea  of  the  upper  ether  (the  fiery  air  of  heaven) 
has  originated  in  the  primary  and  normal  contraries  of  heavy 
and  light,  lower  and  upper,  earth  vxAfire.  These  extremes 

*  Empedocles,  v.  216,  calls  the  ether  irapfavouv,  brightly-beaming, 
and  therefore  self-luminous. 

t  Plato,  Cratyl.,  410  B.,  where  we  meet  with  the  expression  aetdsrip. 
Aristot.,  De  Casio,  1,  3,  p.  270,  Bekk.,  says,  in  opposition  to  Anaxagoras: 
aidtpa  rrpoffuvofiaaav  TOV  UVUTUTU  TOTTOV,  U.TTO  TOT  delv  act  rbv  aldiov 
Xpovov  -QfUfvoi.  TTJV  snuwpiav  avru.  'Avagayopaf  t)e  KaraKixpilfai  ru 
ov6/j.aTi  TovTCf)  ov  KO^uf  •  bvoftd&t  yap  aWepa  avrl  irvpoc..  We  find  this 
more  circumstantially  referred  to  in  Aristot.,  Meteor.,  1,  3,  p.  339,  lines 
21-34,  Bekk. :  "  The  so-called  ether  has  an  ancient  designation,  which 
Anaxagoras  seems  to  identify  with  fire ;  for,  according  to  him,  the  up- 
per region  is  full  of  fire,  and  to  be  considered  as  ether ;  in  which,  in- 
deed, he  is  correct.  For  the  ancients  appear  to  have  regarded  the  body 
which  is  in  a  constant  state  of  movement,  as  possessing  a  divine  nature, 
and  therefore  called  it  ether,  a  substance  with  which  we  have  nothing 
analogous.  Those,  however,  who  hold  the  space  surrounding  bodies  to 
be  fire  no  less  than  the  bodies  themselves,  and  who  look  upon  that 
which  lies  between  the  earth  and  the  stars  as  air,  would  probably  re- 
linquish such  childish  fancies  if  they  properly  investigated  the  results  of 
the  latest  researches  of  mathematicians."  (The  same  etymology  of  this 
word,  implying  rapid  revolution,  is  referred  to  by  the  Aristotelian,  or 
Stoic,  author  of  the  work  De  Mundo,  cap.  2,  p.  392,  Bekk.)  Professor 
Franz  has  correctly  remarked,  "That  the  play  of  words  in  the  designa- 
tion of  bodies  in  eternal  motion  (aufta  uei  dtov')  and  of  the  divine  (tfftov) 
alluded  to  in  the  Meteoroloeica,  is  strikingly  characteristic  of  the  Greek 
type  of  imagination,  and  affords  additional  evidence  of  the  inaptitude  of 
the  ancients  for  etymological  inquiry."  Professor  Buschmann  calls  at- 
tention to  a  Sanscrit  term,  dschtra,  ether  or  the  atmosphere,  which  looks 
very  like  the  Greek  aidr/p,  with  which  it  has  been  compared  by  Vans 
Kennedy,  in  his  Researches  into  the  Origin  and  Affinity  of  the  principal 
Languages  of  Asia  and  Europe,  1828,  p.  279.  This  word  may  also  be 
ich 


referred  to  the  root  (as,  asch),  to  which  the  Indians  attach  the  signifi 
cation  of  shining  or  beaming. 


COSMICAL    ETHER.  33 

are  separated  by  two  intermediate  elementary  conditions,  of 
which  the  one,  water,  approximates  most  nearly  to  the  heavy 
earth,  and  the  other,  air,  to  the  lighter  element  of  fire.* 

Considered  as  a  medium  filling  the  regions  of  space,  the 
ether  of  Empedocles  presents  no  other  analogies  excepting 
those  of  subtlety  and  tenuity  with  the  ether,  by  whose  trans- 
verse vibrations  modern  physicists  have  succeeded  so  hap- 
pily in  explaining,  on  purely  mathematical  principles,  the 
propagation  of  light,  with  all  its  properties  of  double  refrac- 
tion, polarization,  and  interference.  The  natural  philosophy 
of  Aristotle  further  teaches  that  the  ethereal  substance  pen- 
etrates all  the  living  organisms  of  the  earth — both  plants 
and  animals  ;  that  it  becomes  in  these  the  principle  of  vital 
heat,  the  very  germ  of  a  psychical  principle,  which,  uninflu- 
enced by  the  body,  stimulates  men  to  independent  activity.! 
These  visionary  opinions  draw  down  ether  from  the  higher 
regions  of  space  to  the  terrestrial  sphere,  and  represent  it  as 
a  highly  rarefied  substance  constantly  penetrating  through 
the  atmosphere  and  through  solid  bodies  ;  precisely  similar 
to  the  vibrating  light-ether  of  Huygens,  Hooke,  and  modern 
physicists.  But  what  especially  distinguishes  the  older  Ionic 
from  the  modern  hypothesis  of  ether  is  the  original  assump- 
tion of  luminosity,  a  view,  however,  not  entirely  advocated 
by  Aristotle.  The  upper  fire-air  of  Empedocles  is  expressly 
termed  brightly  radiating  (-rrafi^avouv),  and  is  said  to  be 
seen  by  the  inhabitants  of  the  earth  in  certain  phenomena, 
gleaming  brightly  through  fissures  and  chasms  (^da/zara) 
which  occur  in  the  firmament.^ 

The  numerous  investigations  that  have  been  made  in  re- 
cent times  regarding  the  intimate  relation  between  light, 
heat,  electricity,  and  magnetism,  render  it  far  from  improba- 
ble that,  as  the  transverse  vibrations  of  the  ether  which 
fills  the  regions  of  space  give  rise  to  the  phenomena  of  light, 
the  thermal  and  electro-magnetic  phenomena  may  likewise 

•  Aristot.,  De  Ccelo,  iv.,  1,  and  3-4,  p.  308,  and  311-312,  Bekk.  If 
the  Stagirite  withholds  from  ether  the  character  of  a  fifth  element, 
which  indeed  is  denied  by  Ritter  (Geschichte  der  Philosophic,  th.  iii.,  s. 
259),  and  by  Martin  (Etudes  sur  le  Timte  de  Platan.,  t.  ii.,  p.  150),  it  ia 
only  because,  according  to  him,  ether,  as  a  condition  of  matter,  has  no 
contrary.  (Compare  Biese,  Philosophic  des  Aristoteles,  bd.  xi.,  s.  66.) 
Among  the  Pythagoreans,  ether,  as  a  fifth  element,  was  represented  by 
the  fifth  of  the  regular  bodies,  the  dodecahedron,  composed  of  twelve 
pentagons.  (Martin,  t.  ii.,  p.  245-250.) 

t  See  the  proofs  collected  by  Biese,  op.  cit.,  bd.  xi.,  s.  93. 

t  Cosmos,  vol.  i.,  p.  153. 

B2 


34  COSMOS. 

have  their  origin  in  analogous  kinds  of  motion  (currents).  It 
is  reserved  for  future  ages  to  make  great  discoveries  in  ref- 
erence to  these  subjects.  Light,  and  radiating  heat,  which 
is  inseparable  from  it,  constitute  a  main  cause  of  motion  and 
organic  life,  both  in  the  non-luminous  celestial  bodies  and  on 
the  surface  of  our  planet.*  Even  far  from  its  surface,  in 
the  interior  of  the  earth's  crust,  penetrating  heat  calls  forth 
electro-magnetic  currents,  which  exert  their  exciting  influ- 
ence on  the  combinations  and  decompositions  of  matter  —  on 
all  formative  agencies  in  the  mineral  kingdom  —  on  the  dis- 
turbance of  the  equilibrium  of  the  atmosphere  —  and  on  the 
functions  of  vegetable  and  animal  organisms.  If  electricity 
moving  in  currents  develops  magnetic  forces,  and  if,  in  ac- 
cordance with  an  early  hypothesis  of  Sir  "William  Herschel,t 
the  sun  itself  is  in  the  condition  of  "  a  perpetual  northern 
light"  (I  should  rather  say  of  an  electro-magnetic  storm),  we 
should  seem  warranted  in  concluding  that  solar  light,  trans- 
mitted in  the  regions  of  space  by  vibrations  of  ether,  may  be 
accompanied  by  electro-magnetic  currents. 

Direct  observations  on  the  periodic  changes  in  the  decli- 
nation, inclination,  and  intensity  of  terrestrial  magnetism, 
have,  it  is  true,  not  yet  shown  with  certainty  that  these  con- 
ditions are  affected  by  the  different  positions  of  the  sun  or 
moon,  notwithstanding  the  latter's  contiguity  to  the  earth. 
The  magnetic  polarity  of  the  earth  exhibits  no  variations 
that  can  be  referred  to  the  sun,  or  which  perceptibly  affect 
the  precession  of  the  equinoxes.  t  The  remarkable  rotatory 
or  oscillatory  motion  of  the  radiating  cone  of  light  of  Halley's 
comet,  which  Bessel  observed  from  the  12th  to  the  22d  of 
October,  1835,  and  endeavored  to  explain,  led  this  great  as- 
tronomer to  the  conviction  that  there  existed  a  polar  force, 


Compare  the  fine  passage  on  me  influence  of  the  sun's  rays  in  Sir 
n  Herschel's  Outlines  of  Astronomy,  p.  237  :  "  By  the  vivifying  ac- 
tion of  the  sun's  rays,  vegetables  are  enabled  to  draw  support  from  in- 


organic matter,  and  become,  in  their  turn,  the  support  of  animals  and 
of  man,  and  the  sources  of  those  great  deposits  of  dynamical  efficiency 
which  are  laid  up  for  human  use  in  our  coo1,  strata.  By  them  the  wa- 
ters of  the  sea  are  made  to  circulate  in  v*»pT  through  the  air,  and  irri- 
gate the  land,  producing  springs  and  rivers.  By  them  are  produced 
all  disturbances  of  the  chemical  equilibrium  of  the  elements  of  nature, 
which,  by  a  series  of  compositions  and  decompositions,  give  rise  to  new 
products,  and  originate  a  transfer  of  materials." 

t  Philos.  Transact,  for  1795,  vol.  Ixxxv.,  p.  318  ;  John  Herschel,  Out- 
lines  of  Astr.,  p.  238;  see  also  Cosmos,  vol.  i.,  p.  189. 

t  See  Bessel,  in  Schumacher's  Astr.  Nachr.,  bd.  xiii.,  1836,  No.  300, 
B.  201. 


RADIATING  HEAT.  '     35 

"  whose  action  differed  considerably  from  gravitation  or  the 
ordinary  attracting  force  of  the  sun ;  since  those  portions  of 
the  comet  which  constitute  the  tail  are  acted  upon  by  a  re- 
pulsive force  proceeding  from  the  body  of  the  sun."*  The 
splendid  comet  of  1744,  which  was  described  by  Heinsius, 
led  my  deceased  friend  to  similar  conjectures. 

T/te  actions  of  radiating  heat  in  the  regions  of  space  are 
regarded  as  less  problematical  than  electro-magnetic  phenom- 
ena. According  to  Fourier  and  Poisson,  the  temperature  of 
the  regions  of  space  is  the  result  of  radiation  of  heat  from  the 
sun  and  all  astral  bodies,  minus  the  quantity  lost  by  absorp- 
tion in  traversing  the  regions  of  space  filled  with  ether,  t 
Frequent  mention  is  made  in  antiquity  by  the  Greek  and 
RomanJ  writers  of  this  stellar  heat ;  not  only  because,  from 
a  universally  prevalent  assumption,  the  stars  appertained  to 
the  region  of  the  fiery  ether,  but  because  they  were  supposed 
to  be  themselves  of  a  fiery  nature§ — the  fixed  stars  and  the 
sun  being,  according  to  the  doctrine  of  Aristarchus  of  Samos, 
of  one  and  the  same  nature.  In  recent  times,  the  observa- 
tions of  the  above-mentioned  eminent  French  mathemati- 
cians, Fourier  and  Poisson,  have  been  the  means  of  direct- 
ing attention  to  the  average  determination  of  the  tempera- 
ture of  the  regions  of  space  ;  and  the  more  strongly  since  the 
importance  of  such  determinations  on  account  of  the  radia 
tion  of  heat  from  the  earth's  surface  toward  the  vault  of 
heaven  has  at  length  been  appreciated  in  their  relation  to 
all  thermal  conditions,  and  to  the  very  habitability  of  our 
planet.  According  to  Fourier's  Analytic  Theory  of  Heat, 
the  temperature  of  celestial  space  (des  espaces  planetaires 
ou  celestes)  is  rather  below  the  mean  temperature  of  the 
poles,  or  even,  perhaps,  below  the  lowest  degree  of  cold  hith- 
erto observed  in  the  polar  regions.  Fourier  estimates  it  at 
from  — 58°  to  — 76°  (from  — 40°  to  — 48°  Reaum.).  The  icy 
pole  (pole  glacial),  or  the  point  of  the  greatest  cold,  no  more 

*  Bessel,  op.  cif.,  8.  186-192,  229. 

t  Fourier,  Thforie  Analytique  de  la  Chaleur,  1822,  p.  ix.  (Annalet 
de  Chimie  et  de  Physique,  torn,  iii.,  1816,  p.  350;  torn,  iv.,  1817,  p.  128; 
torn,  vi.,  1817,  p.  259 ;  torn,  xiii.,  1820,  p.  418.)  Poisson,  in  his  Thlorie 
Mathematiqve  de  la  Chaleur  (§  196,  p.  436,  $  200,  p.  447,  and  $  228,  p. 
521),  attempts  to  give  the  numerical  estimates  of  the  stellar  heat  (cha- 
leur  stellaire)  lost  by  absorption  in  the  ether  of  the  regions  of  space. 

t  On  the  heating  power  of  the  stars,  see  Aristot.,  De  Meteor.,  1,  3, 
p.  340,  lin.  28  ;  and  on  the  elevation  of  the  atmospheric  strata  at  which 
heat  is  at  the  minimum,  consult  Seneca,  in  Nat.  Qu&st.,  ii.,  10:  ''So- 
periora  enim  afiris  calorem  vicinoruin  siderum  sentiurt." 

$  Plut.,  Deplac.  Philos.,  ii.,  13. 


corresponds  with  the  terrestrial  pole  than  does  the  thermal 
equator,  which  connects  together  the  hottest  points  of  al] 
meridians  with  the  geographical  equator.  Arago  concludes, 
from  the  gradual  decrease  of  mean  temperatures,  that  the 
degree  of  cold  at  the  northern  terrestrial  pole  is  — 13°,  if  the 
maximum  cold  ohserved  by  Captain  Back  at  Fort  Reliance 
(62°  46'  lat.)  in  January,  1834,  were  actually — 70°  ( — 56°-6 
Cent.,  or  — 450>3  Reaum.).*  The  lowest  temperjtlure  that, 
as  far  as  we  know,  has  as  yet  been  observed  on  the  earth,  is 
probably  that  noted  by  Neveroff,  at  Jakutsk  (62°  2'  lat.), 
on  the  21st  of  January,  1838.  The  instruments  used  in 
this  observation  were  compared  with  his  own  by  Middendorff, 
whose  operations  were  always  conducted  with  extreme  ex- 
actitude. Neveroff  found  the  temperature  on  the  day  above 
named  to  be  — 76°  (or  — 48°  Reaum.). 

Among  the  many  grounds  of  uncertainty  in  obtaining  a 
numerical  result  for  the  thermal  condition  of  the  regions  of 
space,  must  be  reckoned  that  of  our  inability  at  present  to 
ascertain  the  mean  of  the  temperatures  of  the  poles  of  great- 
est cold  of  the  two  hemispheres,  owing  to  our  insufficient  ac- 
quaintance with  the  meteorology  of  the  antarctic  pole,  from 
which  the  mean  annual  temperature  must  be  determined.  I 
attach  but  little  physical  probability  to  the  hypothesis  of  Pois- 
son,  that  the  different  regions  of  space  must  have  a  very  va- 
rious temperature,  owing  to  the  unequal  distribution  of  heat- 
radiating  stars,  and  that  the  earth,  during  its  motion  with  the 

*  Arago,  Sur  la  Temperature  du  P6le  et  des  espaces  Celestes,  in  the 
Annuaire  du  Bureau  des  Long,  pour  1825,  p.  189,  et  pour  1834,  p.  192; 
also  Saigey,  Physique  du  Globe,  1832,  p.  60-76.  Swanberg  found,  from 
considerations  on  refraction,  that  the  temperature  of  the  regions  of  space 
was  — 58°.5.  —  Berzelius,  Jahresbericht  fur  1830,  s.  54.  Arago,  from 
polar  observations,  fixed  it  at  — 70° ;  and  Pectet  at  — 76°.  Saigey,  by 
calculating  the  decrease  of  heat  in  the  atmosphere,  from  367  observa- 
tions made  by  myself  in  the  chain  of  the  Andes  and  in  Mexico,  found  it 
— 85° ;  and  from  thermometrical  measurements  made  at  Mont  Blanc, 
and  during  the  aeronautic  ascent  of  Gay-Lussac,  — 107°-2.  Sir  John 
Herschel  (Edinburgh  Review,  vol.  87,  1848,  p.  223)  gives  it  at  —132°. 
We  feel  considerable  surprise,  and  have  our  faith  in  the  correctness  of 
the  methods  hitherto  adopted  somewhat  shaken,  when  we  find  that 
Poisson,  notwithstanding  that  the  mean  temperature  of  Melville  Island 
(74°  47'  N.  lat.)  is  — 1°  66',  gives  the  mean  temperature  of  the  regions 
of  space  at  only  8°'6,  having  obtained  his  data  from  purely  theoretical 
premises,  according  to  which  the  regions  of  space  are  warmer  than  the 
outer  limits  of  the  atmosphere  (see  the  work  already  referred  to,  $  227, 
p.  520) ;  while  Pouillet  states  it,  from  actinometric  experiments,  to  be 
as  low  as  — 223°-6.  See  Comptet  Rendus  de  I' Academic  det  Science!, 
torn,  vii.,  1838,  p.  25-65. 


TEMPERATURE    OF    SPACE.  37 

whole  solar  system,  receives  its  internal  heat  from  without 
while  passing  through  hot  and  cold  regions.* 

The  question  whether  the  thermal  conditions  of  the  celes- 
tial regions,  and  the  climates  of  individual  portions  of  space, 
have  suffered  important  variations  in  the  course  of  ages,  de 
pends  mainly  on  the  solution  of  a  problem  warmly  discussed 
by  Sir  William  Herschel :  whether  the  nebulous  masses  are 
subjected  to  progressive  processes  of  formation,  while  the  cos- 
mic al  vapor  is  being  condensed  around  one  or  more  nuclei  in 
accordance  with  the  laws  of  attraction  ?  By  such  a  con- 
densation of  cosmical  vapor,  heat  must  be  liberated,  as  in 
every  transition  of  gases  and  fluids  into  a  state  of  solidifica- 
tion.t  If,  in  accordance  with  the  most  recent  views,  and 
the  important  observations  of  Lord  Rosse  and  Mr.  Bond,  we 
may  assume  that  all  nebulae,  including  those  which  the  high- 
est power  of  optical  instruments  has  hitherto  failed  in  resolv- 
ing, are  closely  crowded  stellar  swarms,  our  faith  in  this  per- 
petually augmenting  liberation  of  heat  must  necessarily  be 
in  some  degree  weakened.  But  even  small  consolidated  cos- 
mical bodies  which  appear  on  the  field  of  the  telescope  as 
distinguishable  luminous  points,  may  change  their  density 
by  combining  in  larger  masses  ;  and  many  phenomena  pre- 
sented by  our  own  planetary  system  lead  to  the  conclusion 
that  planets  have  been  solidified  from  a  state  of  vapor^  and 
that  their  internal  heat  owes  its  origin  to  the  formative  pro- 
cess of  conglomerated  matter. 

It  may  at  first  sight  seem  hazardous  to  term  the  fearfully 
low  temperature  of  the  regions  of  space  (which  varies  be- 
tween the  freezing  point  of  mercury  and  that  of  spirits  of 
wine)  even  indirectly  beneficial  to  the  habitable  climates  of 
the  earth  and  to  animal  and  vegetable  life.  But  in  proof  of 
the  accuracy  of  the  expression,  we  need  only  refer  to  the  ac- 
tion of  the  radiation  of  heat.  The  sun-warmed  surface  of 
our  planet,  as  well  as  the  atmosphere  to  its  outermost  strata, 
freely  radiate  heat  into  space.  The  loss  of  heat  which  they 
experience  arises  from  the  difference  of  temperature  between 
the  vault  of  heaven  and  the  atmospheric  strata,  and  from  the 
feebleness  of  the  counter-radiation.  How  enormous  would 
be  this  loss  of  heat.J  if  the  regions  of  space,  instead  of  the 

*  See  Poisson,  Tklorie  Maih6m.  de  la  Chaleur,  p.  438.  According 
to  him,  the  consolidation  of  the  earth's  strata  began  from  the  center,  ana 
advanced  gradually  toward  the  surface ;  $  193,  p.  429.  Compare  also 
Cosmos,  vol.  i.,  p.  176,  177.  t  Cosmos,  vol.  i.,  p.  83,  84,  144. 

t  "  Were  there  no  atmosphere,  a  thermometer  freely  exposed  (at  sun- 


38  COSMOS. 

temperature  they  now  possess,  and  which  we  designate  as 
— 76°  of  a  mercury  thermometer,  had  a  temperature  of  about 
— 1400°  or  even  many  thousand  times  lower  ! 

It  still  remains  for  us  to  consider  two  hypotheses  in  rela- 
tion to  the  existence  of  a  fluid  filling  the  regions  of  space, 
of  which  one — the  less  firmly-based  hypothesis—  -refers  to  the 
limited  transparency  of  the  celestial  regions  ;  and  the  other, 
founded  on  direct  observation  and  yielding  numerical  results, 
is  deduced  from  the  regularly  shortened  periods  of  revolution 
of  Encke's  comet.  Olbers  in  Bremen,  and,  as  Struve  has  ob- 
served, Loys  de  Cheseaux  at  Geneva,  eighty  years  earlier* 
drew  attention  to  the  dilemma,  that  since  we  could  not  con- 
ceive any  point  in  the  infinite  regions  of  space  unoccupied  by 
a  fixed  star,  i.  e.,  a  sun,  the  entire  vault  of  heaven  must  ap- 
pear as  luminous  as  our  sun  if  light  were  transmitted  to  us 
in  perfect  intensity  ;  or,  if  such  be  not  the  case,  we  must  as- 
sume that  light  experiences  a  diminution  of  intensity  in  its 
passage  through  space,  this  diminution  being  more  excessive 
than  in  the  inverse  ratio  of  the  square  of  the  distance.  As 
we  do  not  observe  the  whole  heavens  to  be  almost  uniformly 
illumined  by  such  a  radiance  of  light  (a  subject  considered 
by  Halleyf  in  an  hypothesis  which  he  subsequently  rejected), 
the  regions  of  space  can  not,  according  to  Cheseaux,  Olbers, 
and  Struve,  possess  perfect  and  absolute  transparency.  The 
results  obtained  by  Sir  William  Herschel  from  gauging  the 

«p 

set)  to  the  heating  influence  of  the  earth's  radiation,  and  the  cooling 
power  of  its  own  into  space,  would  indicate  a  medium  temperature  be- 
tween that  of  the  celestial  spaces  (—132°  Fahr.)  and  that  of  the  earth's 
surface  below  it,  82°  Fahr.,  at  the  equator,  3*°  Fahr.,  in  the  Polar  Sea. 
Under  the  equator,  then,  it  would  stand,  on  the  average,  at  — 25°  Fahr., 
and  in  the  Polar  Sea  at  — 68°  Fahr.  The  presence  of  the  atmosphere 
tends  to  prevent  the  thermometer  so  exposed  from  attaining  these  ex- 
treme low  temperatures :  first,  by  imparting  heat  by  conduction ;  sec- 
ondly, by  impeding  radiation  outward." — Sir  John  Herschel,  in  the 
Edinburgh  Review,  vol.  87,  1848,  p.  222.  "  Si  la  chaleur  des  espaces 
planetaires  n'existait  point,  notre  atmosphere  6prouverait  un  refroidis- 
sement,  dont  on  ne  peut  fixer  la  limite.  Probablement  la  vie  des  plantes 
et  des  animaux  serait  impossible  a  la  surface  du  globe,  ou  releguee  dans 
une  etroite  zone  de  cette  surface."  (Saigey,  Physique  du  Globe,  p.  77.) 

*  Traiti  de  la  Comete  de  1743,  avec  une  Addition  sur  la  force  de  la 
Lumiere  et  sa  Propagation  dans  l'6ther,  ct  sur  la  distance  des  etoiles fixes; 
par  Loys  de  Cheseaux  (1744).  On  the  transparency  of  the  regions  of 
space,  see  Olbers,  in  Bode's  Jahrbuckfur  1826,  s.  110-121 ;  and  Struve, 
Etudes  d'Astr.  Slellaire,  1847,  p.  83-93,  and  note  95.  Compare  also 
Sir  John  Herschel,  Outlines  of  Astronomy,  $  798,  and  Cosmos,  vol.  i.,  p. 
151,  152. 

t  Halley,  On  the  Infinity  of  the  Sphere  of  Fixed  Stars,  in  the  Philos. 
Transact.,  vol.  xxxi.,  for  tfie  year  1720,  p.  22-26. 


RESISTING    MEDIUM.  39 

stars,*  and  from  his  ingenious  experiments  on  the  space-pen- 
etrating power  of  his  great  telescopes,  seem  to  show,  that  if 
the  light  of  Sirius  in  its  passage  to  us  through  a  gaseous  or 
ethereal  fluid  loses  only  T£7tb  of  its  intensity,  this  assump- 
tion, which  gives  the  amount  of  the  density  of  a  fluid  capa- 
ble of  diminishing  light,  would  suffice  to  explain  the  phe- 
nomena as  they  manifest  themselves.  Among  the  doubts 
advanced  by  the  celebrated  author  of  "  The  New  Outlines 
of  Astronomy"  against  the  views  of  Olbers  and  Struve,  one 
of  the  most  important  is  that  his  twenty -feet  telescope  shows, 
throughout  the  greater  portion  of  the  Milky  Way  in  both  hem- 
ispheres, the  smallest  stars  projected  on  a  black  ground. t 

A  better  proof,  and  one  based,  as  we  have  already  stated, 
upon  direct  observation  of  the  existence  of  a  resisting  fluid,} 
is  afforded  by  Encke's  comet,  and  by  the  ingenious  and  im- 
portant conclusion  to  which  my  friend  was  led  in  his  observ- 
ations on  this  body.  This  resisting  medium  must,  however, 
be  regarded  as  different  from  the  all-penetrating  light-ether, 
because  the  former  is  only  capable  of  offering  resistance  in- 
asmuch as  it  can  not  penetrate  through  solid  matter.  These 
observations  require  the  assumption  of  a  tangential  force  to 
explain  the  diminished  period  of  revolution  (the  diminished 
major  axis  of  the  ellipse),  and  this  is  most  directly  afforded 
by  the  hypothesis  of  a  resisting  fluid. §  The  greatest  action 

*  Cosmos,  vol.  i.,  p.  86,  87. 

t  "Throughout  by  far  the  larger  portiou  of  the  extent  of  the  Milky 
Way  in  both  hemispheres,  the  general  blackness  of  the  ground  of  the 
heavens,  on  which  its  stars  are  projected  ....  In  those  regions  where 
the  zone  is  clearly  resolved  into  stars,  well  separated,  and  seen  projected 
on  a  black  ground,  and  where  we  look  out  beyond  them  into  space. . . ." 
—Sir  John  Herschel,  Outlines  of  Astr.,  p.  537,  539. 

t  Cosmos,  vol.  i.,  p.  85,  86, 107 ;  compare  also  Laplace,  Essai  Philos- 
ophique  sur  les  Probability's,  1825,  p.  133 ;  Arago,  in  the  Annuaire  du 
Bureau  des  Long,  pour  1832,  p.  188,  pour  1836,  p.  216;  and  Sir  John 
Herschel,  Outlines  of  Astr.,  $  577. 

§  The  oscillatory  movement  of  the  emanations  from  the  head  of  some 
comets,  as  in  that  of  1744,  and  in  Halley's,  as  observed  by  Bessel,  be- 
tween the  12th  and  22d  of  October,  1835  (Schumacher,  Astron.  Nachr., 
Nos.  300,  302,  §  185,  232),  "may  indeed,  in  the  case  of  some  individ- 
uals of  this  class  of  cosmical  bodies,  exert  an  influence  on  the  transla- 
tory  and  rotatory  motion,  and  lead  us  to  infer  the  action  of  polar  forces 
(§  201, 229),  which  differ  from  the  ordinary  attracting  force  of  the  sun ;" 
but  the  regular  acceleration  observable  for  sixty-three  years  in  Encke's 
comet  (whose  period  of  revolution  is  3§  years),  can  not  be  regarded  as 
the  result  of  incidental  emanations.  Compare,  on  this  cosmically  im- 
portant subject,  Bessel,  in  Schum.,  Astron.  Nachr.,  No.  289,  s.  6,  and 
No.  310,  s.  345-350,  with  Encke's  Treatise  on  the  hypothesis  of  the  re- 
sisting medium,  in  Schum.,  No.  305,  s.  265-274 


40  COSMOS. 

is  manifested  during  the  twenty-five  days  immediately  pre- 
ceding and  succeeding  the  comet's  perihelion  passage.  The 
value  of  the  constant  is  therefore  somewhat  different,  because 
in  the  neighborhood  of  the  sun  the  highly  attenuated  but 
still  gravitating  strata  of  the  resisting  fluid  are  denser.  01- 
bers  maintained*  that  this  fluid  could  not  be  at  rest,  but 
must  rotate  directly  round  the  sun,  and  therefore  the  resist- 
ance offered  to  retrograde  comets,  like  Halley's,  must  differ 
wholly  from  that  opposed  to  those  comets  having  a  direct 
course,  like  Encke's.  The  perturbations  of  comets  having 
long  periods  of  revolution,  and  the  difference  of  their  magni 
tudes  and  sizes,  -complicate  the  results,  and  render  it  diffi- 
cult to  determine  what  is  ascribable  to  individual  forces. 

The  gaseous  matter  constituting  the  belt  of  the  zodiacal 
light  may,  as  Sir  John  Herschelf  expresses  it,  be  merely  the 
denser  portion  of  this  comet-resisting  medium.  Although  it 
may  be  shown  that  all  nebulae  are  crowded  stellar  masses, 
indistinctly  visible,  it  is  certain  that  innumerable  comets  fill 
the  regions  of  space  with  matter  through  the  evaporation  of 
their  tails,  some  of  which  have  a  length  of  56, 000, 000  of 
miles.  Arago  has  ingeniously  shown,  on  optical  grounds,^ 
that  the  variable  stars  which  always  exhibit  white  light 
without  any  change  of  color  in  their  periodical  phases,  might 
afford  a  means  of  determining  the  superior  limit  of  the  dens- 
ity to  be  assumed  for  cosmical  ether,  if  we  suppose  it  to  be 
equal  to  gaseous  terrestrial  fluids  in  its  power  of  refraction. 

The  question  of  the  existence  of  an  ethereal  fluid  filling 
the  regions  of  space  is  closely  connected  with  one  warmly 
agitated  by  WolJaston,§  in  reference  to  the  definite  limit  of 
the  atmosphere — a  limit  which  must  necessarily  exist  at  the 
elevation  where  the  specific  elasticity  of  the  air  is  equipoised 
by  the  force  of  gravity.  Faraday's  ingenious  experiments  on 

*  Gibers,  in  Schum.,  Astr.  NacJir.,  No.  268,  a.  58. 

t  Outlines  of  Astronomy,  $  556,  597. 

t  "En  assimilant  la  mature  ires  rare  qui  remplit  les  espaces  celestes 
quant  a  ses  proprietes  refringentes  aux  gas  terrestres,  la  densite  de  cette 
matiere  nt  saurait  depasser  itne  certaine  limite  dont  les  observations  des 
eloilcs  chcngeantes,  p.  e.  celles  d1  Algol  oudc/3  de  Persic,  peuvent  assigner 
la  valeur." — Arago,  in  the  Annuaire  pour  1842,  p.  336-345.  "  On  com 
paring  the  extremely  rare  matter  occupying  the  regions  of  space  with 
terrestrial  gases,  in  respect  to  its  refractive  properties,  we  shall  find  that 
the  density  of  this  matter  can  not  exceed  a  definite  limit,  whose  value 
may  be  obtained  from  observations  of  variable  stars,  as,  for  instance, 
Algol  or  (3  Persei." 

§  See  Wollaston,  Philos.  Transact,  for  1822,  p.  89,'  Sir  John  Herschel, 
op.  eit.,  $  34,  36. 


FIRST    TELESCOPE,  41 

the  limits  of  an  atmosphere  of  mercury  (that  is,  the  elevation 
at  which  mercurial  vapors  precipitated  on  gold  leaf  cease 
perceptibly  to  rise  in  an  air-filled  space)  have  given  consid- 
erable weight  to  the  assumption  of  a  definite  surface  of  the 
atmosphere  "  similar  to  the  surface  of  the  sea."  Can  any 
gaseous  particles  belonging  to  the  region  of  space  blend  with 
our  atmosphere  and  produce  meteorological  changes  ?  New- 
ton* inclined  to  the  idea  that  such  might  be  the  case.  If 
we  regard  falling  stars  and  meteoric  stones  as  planetary  as- 
teroids, we  may  be  allowed  to  conjecture  that  in  the  streams 
of  the  so-called  November  phenomena,!  when,  as  in  1799, 
1833,  and  1834,  myriads  of  falling  stars  traversed  the  vault 
of  heaven,  and  northern  lights  were  simultaneously  observed, 
our  atmosphere  may  have  received  from  the  regions  of  space 
some  elements  foreign  to  it,  which  were  capable  of  exciting 
electro-magnetic  processes. 


II. 

NATURAL  AND  TELESCOPIC  VISION.— SCINTILLATION  OF  THE  STARS 
—VELOCITY  OF  LIGHT.— RESULTS  OF  PHOTOMETRY. 

THE  increased  power  of  vision  yielded  nearly  two  hundred 
and  fifty  years  ago  by  the  invention  of  the  telescope,  has  af- 
forded to  the  eye,  as  the  organ  of  sensuous  cosmical  contem- 
plation, the  noblest  of  all  aids  toward  a  knowledge  of  the 
contents  of  space,  and  the  investigation  of  the  configuration, 
physical  character,  and  masses  of  the  planets  and  their  sat- 
ellites. The  first  telescope  was  constructed  in  1608,  seven 
years  after  the  death  of  the  great  observer,  Tycho  Brahe. 
Its  earliest  fruits  were  the  successive  discovery  of  the  satel- 
lites of  Jupiter,  the  Sun's  spots,  the  crescent  shape  of  Venus, 
the  ring  of  Saturn  as  a  triple  planetary  formation  (planeta 
tergeminus),  telescopic  stellar  swarms,  and  the  nebulae  in 
Andromeda. J  In  1634,  the  French  astronomer  Morin,  emi- 
nent for  his  observations  on  longitude,  first  conceived  the  idea 
of  mounting  a  telescope  on  the  index  bar  of  an  instrument 
of  measurement,  and  seeking  to  discover  Arcfurus  by  day.$ 

*  Newton,  Princ.  Mathem.,  t.  iii.  (1760),  p.  671:  "Vapores  qui  ex 
sole  et  stellis  fixis  et  caudis  cometarum  oriuiitur,  incidere  posswit  in  at- 
mosphaeras  planetarum "  t  Cosmos,  vol.  i.,  p.  124-135. 

t  See  Cosmos,  vol.  ii.,  p.  317-335,  with  notes. 

$  Delambre,  Histoire  de  C  Astronomic  Moderne,  torn,  ii.,  p.  255,  269 


42  COSMOS. 

The  perfection  in  the  graduation  of  the  arc  would  have  failed 
entirely,  or  to  a  considerable  extent,  in  affording  that  great- 
er precision  of  observation  at  which  it  aimed,  if  optical  and 
astronomical  instruments  had  not  been  brought  into  accord, 
and  the  correctness  of  vision  made  to  correspond  with  that 
of  measurement.  The  micrometer-application  of  fine  threads 
stretched  in  the  focus  of  the  telescope,  to  which  that  instru- 
ment owes  its  real  and  invaluable  importance,  was  first  de- 
vised, six  years  afterward  (1640),  by  the  young  and  talented 
Gascoigne.* 

While,  as  I  have  already  observed,  telescopic  vision,  ob- 
servation, and  measurement  extend  only  over  a  period  of 
about  240  years  in  the  history  of  astronomical  science,  we 
find,  without  including  the  epoch  of  the  Chaldeans,  Egyp- 
tians, and  Chinese,  that  more  than  nineteen  centuries  have 
intervened  between  the  age  of  Timochares  and  Aristillusf 
and  the  discoveries  of  Galileo,  during  which  period  the  posi- 
tion and  course  of  the  stars  were  observed  by  the  eye  alone, 
unaided  by  instruments.  When  we  consider  the  numerous 
disturbances  which,  during  this  prolonged  period,  checked  the 
advance  of  civilization,  and  the  extension  of  the  sphere  of 
ideas  among  the  nations  inhabiting  the  basin  of  the  Medi- 
terranean, we  are  astonished  that  Hipparchus  and  Ptolemy 
should  have  been  so  well  acquainted  with  the  precession  of 
the  equinoxes,  the  complicated  movements  of  the  planets,  the 
two  principal  inequalities  of  the  moon,  and  the  position  of  the 
stars  ;  that  Copernicus  should  have  had  so  great  a  knowledge 
of  the  true  system  of  the  universe ;  and  that  Tycho  Brahe 
should  have  been  so  familiar  with  the  methods  of  practical 
astronomy  before  the  discovery  of  the  telescope.  Long  tubes, 

272.  Morin,  in  his  work,  Seientia  Longitudinum,  which  appeared  in 
1634,  writes  as  follows:  Applicatio  tubi  optici  ad  alkidadam  pro  slellit 
fans  prompte  et  accurate  mensurandis  a  me  excogitata  est.  Picard  had 
not,  up  to  the  year  1667,  employed  any  telescope  on  the  mural  circle; 
and  Hevelius,  when  Halley  visited  him  at  Dantzic  in  1679,  and  admired 
the  precision  of  his  measurement  of  altitudes,  was  observing  through 
improved  slits  or  openings.  (Daily's  Catal.  of  Stars,  p.  38.) 

*  The  unfortunate  Gascoigne,  whose  merits,  remained  so  long  unac- 
knowledged, lost  his  life,  when  scarcely  twenty-three  years  of  age,  at 
the  battle  of  Marston  Moor,  fought  by  Cromwell  against  the  Royalists. 
See  Derham,  in  the  Philos.  Transact.,  vol.  xxx.,  for  1717-1719,  p.  603 
-610.  To  him  belongs  the  merit  of  a  discovery  which  was  long  ascribed 
to  Picard  and  Auzout,  and  which  has  given  an  impulse  previously  un- 
known to  practical  astronomy,  the  principal  object  of  which  is  to  de- 
termine positions  in  the  vault  of  heaven. 

t  Cosmos,  vol.  iL,  p.  177,  1F8. 


DIOPTRIC   TUBES.  43 

which  were  certainly  employed  by  Arabian  astronomers,  and 
very  probably  also  by  the  Greeks  and  Romans,  may  indeed, 
in  some  degree,  have  increased  the  exactness  of  the  observa- 
tions by  causing  the  object  to  be  seen  through  diopters  or  slits. 
Abul-Hassan  speaks  very  distinctly  of  tubes,  to  the  extremi- 
ties of  which  ocular  and  object  diopters  were  attached  ;  and 
instruments  so  constructed  were  used  in  the  observatory 
founded  by  Hulagu  at  Meragha.  If  stars  be  more  easily 
discovered  during  twilight  by  means  of  tubes,  and  if  a  star 
be  sooner  revealed  to  the  naked  eye  through  a  tube  than 
without  it,  the  reason  lies,  as  Arago  has  already  observed,  in 
the  circumstance  that  the  tube  conceals  a  great  portion  of  the 
disturbing  light  (rayons  perturbateurs)  diffused  in  the  atmos 
pheric  strata  between  the  star  and  the  eye  applied  to  the  tube. 
In  like  manner,  the  tube  prevents  the  lateral  impression  of  the 
faint  light  which  the  particles  of  air  receive  at  night  from  all 
the  other  stars  in  the  firmament.  The  intensity  of  the  image 
and  the  size  of  the  star  are  apparently  augmented.  In  a  fre- 
quently emendated  and  much  contested  passage  of  Strabo,  in 
which  mention  is  made  of  looking  through  tubes,  this  "  en- 
larged form  of  the  stars"  is  expressly  mentioned,  and  is  erro- 
neously ascribed  to  refraction.* 

*  The  passage  in  which  Strabo  (lib.  iii.,  p.  138,  Casaub.)  attempts  to 
refute  the  views  of  Posidonius  is  given  as  follows,  according  to  the 
manuscripts :  "  The  image  of  the  sun  is  enlarged  on  the  seas  at  its  ris- 
ing as  well  as  at  its  setting,  because  at  these  times  a  larger  mass  of  ex- 
halations rises  from  the  humid  element ;  and  the  eye,  looking  through 
these  exhalations,  sees  images  refracted  into  larger  forms,  as  observed 
through  lubes.  The  same  thing  happens  when  the  setting  sun  or  moon 
is  seen  through  a  dry  and  thin  cloud,  when  those  bodies  likewise  appear 
reddish."  This  passage  has  recently  been  pronounced  corrupt  (see 
Kramer,  in  Strabonis  Geogr.,  1844,  vol.  i.,  p.  211),  and  81  vdAwv  (through 
glass  spheres)  substituted  for  61  avhuv  (Schneider,  Eclog.  Phyt.,  vol.  ii., 
p.  273).  The  magnifying  power  of  hollow  glass  spheres,  filled  with 
water  (Seneca,  i.,  6),  was,  indeed,  as  familiar  to  the  ancients  as  the  ac- 
tion of  burning-glasses  or  crystals  (Aristoph.,  Nub.,  v.  765),  and  that  of 
Nero's  emerald  (Plin.,  xxxvii.,  5);  but  these  spheres  most  assuredly 
could  not  have  been  employed  as  astronomical  measuring  instruments. 
(Compare  Cosmos,  vol.  ii.,  p.  245,  and  note  J.)  Solar  altitudes,  taken 
through  thin,  light  clouds,  or  through  volcanic  vapors,  exhibit  no  trace 
of  the  influence  of  refraction.  (Humboldt,  Recveil  d'Obterv.  Astr.,  vol. 
i.,  p.  123.)  Colonel  Baeyer  observed  no  angular  deviation  in  the  heli- 
otrope light  on  the  passage  of  streaks  of  mist,  or  even  from  artificially 
developed  vapors,  and  therefore  fully  confirms  Arago's  experiments. 
Peters,  at  Pulkowa,  in  no  case  found  a  diiference  of  0"'017  on  compar- 
ing groups  of  stellar  altitudes,  measured  in  a  clear  sky,  and  through 
light  clouds.  See  his  Recherche*  sur  la  Parallaxe  des  Etoiles,  1848,  p. 
80,  140-143  ;  also  Struve's  Etudes  Stellaires,  p.  98.  On  the  application 
of  tubes  for  astronomical  observation  in  Arabian  instruments,  see  Jour- 


44  COSMOS. 

Light,  from  whatever  source  it  comes — whether  from  th« 
sun,  as  solar  light,  or  reflected  from  the  planets ;  from  the 
fixed  stars ;  from  putrescent  wood  ;  or  as  the  product  of  the 
vital  activity  of  glow-worms — always  exhibits  the  same  con- 
ditions of  refraction.*  But  the  prismatic  spectra  yielded  by 
different  sources  of  light  (as  the  sun  and  the  fixed  stars)  ex- 
hibit a  difference  in  the  position  of  the  dark  lines  (raies  du 
spectre)  which  Wollaston  first  discovered  in  1808,  and  the  po- 
sition of  which  was  twelve  years  afterward  so  accurately  de- 
termined by  Fraunhofer.  While  the  latter  observer  counted 
600  dark  lines  (breaks  or  interruptions  in  the  colored  spec- 
trum), Sir  David  Brewster,  by  his  admirable  experiments  with 
nitric  oxyd,  succeeded,  in  1833,  in  counting  more  than  2000 
lines.  It  had  been  remarked  that  certain  lines  failed  in  the 
spectrum  at  some  seasons  of  the  year ;  but  Sir  David  Brew- 
ster has  shown  that  this  phenomenon  is  owing  to  different  al- 
titudes of  the  sun,  and  to  the  different  absorption  of  the  rays 
of  light  in  their  passage  through  the  atmosphere.  In  the  spec- 
dam,  Sur  V Obseroatoire  de  Meragha,  p.  27 ;  and  A.  Sedillot,  Mem.  sur 
les  Instruments  Astronomiques  des  Arabes,  1841,  p.  198.  Arabian  astron- 
omers have  also  the  merit  of  having  first  employed  large  gnomons  with 
small  circular  apertures.  In  the  colossal  sextant  of  Abu  Mohammed 
al-Chokandi,  the  limb,  which  was  divided  into  intervals  of  five  minutes, 
received  the  image  of  the  sun.  "  A  midi  les  rayons  du  soleil  passaient 
par  une  ouverture  pratique  dans  la  voflte  de  1'observatoire  qui  couvrait 
{'instrument,  suivaut  le  tuyau,  et  formaient  sur  la  concavite  du  sextant 
une  image  circulaire,  dont  le  centre  donnait,  sur  1'arc  gradue,  le  com 
plement  de  la  hauteur  du  soleil.  Cet  instrument  differe  de  notre  mural, 
qu'en  ce  qu'il  etait  garni  d'un  simple  tuyau  au  lieu  d'une  lunette."  "  At 
noon,  the  rays  of  the  sun  passed  through  an  opening  in  the  dome  of  the 
observatory,  above  the  instrument,  and,  following  the  tube,  formed  in 
the  concavity  of  the  sextant  a  circular  image,  the  center  of  which  marked 
the  sun's  altitude  on  the  graduated  limb.  This  instrument  in  no  way 
differed  from  our  mural  circle,  excepting  that  it  was  furnished  with  a 
mere  tube  instead  of  a  telescope."— Sedillot,  p.  37,  202,  205.  Dioptric 
rulers  (pinnulce)  were  used  by  the  Greeks  and  Arabs  in  determining 
the  moon's  diameter,  and  were  constructed  in  such  a  manner  that  the 
circular  aperture  in  the  moving  object  diopter  was  larger  than  that 
of  the  fixed  ocular  diopter,  and  was  drawn  out  until  the  lunar  disk,  seen 
through  the  ocular  aperture,  completely  filled  the  object  aperture. — 
Delambre,  Hist,  de  VAstron.  du  Moyen  Age,  p.  201 ;  and  S6dillot,  p.  198. 
The  adjustment  of  the  dioptric  rulers  of  Archimedes,  with  round  aper- 
tures or  slits,  in  which  the  direction  of  the  shadows  of  two  small  cylin- 
ders attached  to  the  same  index  bar  was  noted,  seems  to  have  been  orig- 
inally introduced  by  Hipparchus.  (Baily,  Hist,  de  VAstron.  Mod.,  2d 
ed.,  1785,  torn,  i.,  p.  480.)  Compare  also  Theon  Alexandria,  Bas.,  1538, 
p.  257,  262;  Les  Hypotyp.  de  Prochis  Diadockus,  ed.  Halma,  1820,  p 
107,  110  ;  and  Ptolem.  Almag.,  ed.  Halma,  torn,  i.,  Par.,  1813,  p.  Ivii. 
*  According  to  Arago.  See  Moigno,  Rtpert.  d'Optique  Moderne,  1847 
p.  153. 


POLARIZATION    OF    LIGHT.  45 

tra  of  the  light  reflected  from  the  moon,  from  Venus,  Mars, 
and  the  clouds,  we  recognize,  as  might  be  anticipated,  all  the 
peculiarities  of  the  solar  spectrum ;  but,  on  the  other  hand, 
the  dark  lines  in  the  spectrum  of  Sirius  differ  from  those  of 
Castor  and  the  other  fixed  stars.  Castor  likewise  exhibits  dif- 
ferent lines  from  Pollux  and  Procyon.  Amici  has  confirmed 
this  difference,  which  was  first  indicated  by  Fraunhofer,  and 
has  ingeniously  called  attention  to  the  fact  that  in  fixed  stars, 
which  now  have  an  equal  and  perfectly  white  light,  the  dark 
lines  are  not  the  same.  A  wide  and  important  field  is  thus 
still  open  to  future  investigations,*  for  we  have  yet  to  distin- 
guish between  that  which  has  been  determined  with  certain- 
ty and  that  which  is  merely  accidental  and  depending  on  the 
absorbing  action  of  the  atmospheric  strata. 

We  must  here  refer  to  another  phenomenon,  which  is  pow- 
erfully influenced  by  the  specific  character  of  the  source  of 
light.  The  light  of  incandescent  solid  bodies,  and  the  light 
of  the  electric  spark,  exhibit  great  diversity  in  the  number 
and  position  of  Wollaston's  dark  lines.  From  Wheatstone's 
remarkable  experiments  with  revolving  minors,  it  would  ap- 
pear that  the  tight  of  frictional  electricity  has  a  greater  veloc- 
ity than  solar  light  in  the  ratio  of  3  to  2  ;  that  is  to  say,  a  ve- 
locity of  95,908  miles  in  one  second. 

The  stimulus  infused  into  all  departments  of  optical  science 
by  the  important  discovery  of  polarization,!  to  which  the  in- 
genious Malus  was  led  in  1808  by  a  casual  observation  of  the 
light  of  the  setting  sun  reflected  from  the  windows  of  the  Pa- 
lais du  Luxembourg,  has  aflbrded  unexpected  results  to  sci- 
ence by  the  more  thorough  investigation  of  the  phenomena  of 
double  refraction,  of  ordinary  (Huygens's)  and  of  chromatic  po- 
larization, of  interference,  and  of  diffraction  of  light.  Among 
these  results  may  be  reckoned  the  means  of  distinguishing 
between  direct  and  reflected  light,  $  the  power  of  penetrating, 

*  On  the  relation  of  the  dark  lines  on  the  solar  spectrum  in  the  Da- 
guerreotype, see  Comptes  Rendus des  S6ance»  de  I'Acadtmie  des  Science*, 
torn,  xiv.,  1842,  p.  902-904,  and  torn,  xvi.,  1843,  p.  402-407. 

t  Cosmos,  vol.  ii.,  p.  332. 

t  Arago's  investigation  of  cometary  light  may  hero  be  adduced  as  an 
instance  of  the  important  difference  between  proper  and  reflected  light. 
The  formation  of  the  complementary  colors,  red  and  green,  showed  by 
the  application  of  his  discovery  (in  1811)  of  chromatic  polarization,  that 
the  light  of  Halley's  comet  (1835)  contained  reflected  solar  light.  I  was 
myself  present  at  the  earlier  experiments  for  comparing,  by  means  of 
the  equal  and  unequal  intensity  of  the  images  of  the  polariscope,  the 
proper  light  of  Capella  with  the  splendid  comet,  as  it  suddenly  emerged 
from  the  rays  of  the  sun  at  the  beginning  of  July,  1819.  (See  Annuaire 


46  COSMOS. 

as  it  were,  into  the  constitution  of  the  body  of  the  eun  and 
of  its  luminous  envelopes,*  of  measuring  the  pressure  of  at- 

du  Bureau  des  Long,  pour  1836,  p.  232  ;  Cosmos,  vol.  i.,  p.  105  ;  aud  Bes- 
eel,  in  Schumacher's  Jahrbuchfur  1837,  1G9.) 

*  Lettre  de  M.  Arago  a  M.  Alexandre  de  Humboldt,  1840,  p.  37  :  "A 
1'aide  d'un  polariscope  de  mon  invention,  je  reconnus  (avant  1820)  quo 
la  lumiere  de  tous  les  corps  terrestres  incandescents,  solides  ou  liquides, 
est  de  la  lumiere  naturelle,  tant  qu'elle  emane  du  corps  sous  des  inci- 
dences perpendiculaires.  La  lumiere,  au  contraire,  qui  sort  de  la  surface 
incandescente  sous  un  angle  aigu,  offre  des  marques  manifestos  de  po- 
larisation. Je  ne  m'arrete  pas  a  te  rappeler  ici,  comment  je  d6duisis 
de  ce  fait  la  consequence  curieuse  que  la  lumiere  ne  s'eugendre  pas 
seulement  a  la  surface  des  corps ;  qu'une  portion  nalt  dans  leur  sub- 
ttance  ineme,  cette  substance  fut-elle  du  platine.  J'ai  seulement  besoin 
de  dire  qu'en  repetant  la  meme  serie  d'epreuves,  et  avec  les  m£mes 
instruments  sur  la  lumiere  que  lance  une  substance  gazeuse  enflammee, 
on  ne  lui  trouve,  sous  quelque  incllnaison  que  ce  soit,  aucun  des  carac- 
teres  de  la  lumiere  polarisee;  que  la  lumiere  des  gaz,  prise  a  la  sortie 
de  la  surface  enflammee,  est  de  la  lumiere  naturelle,  ce  qui  n'empeche 
pas  qu'elle  ne  se  polarise  ensuite  completement  si  on  la  soumet  a  des 
reflexions  ou  a  des  refractions  conveuables.  De  la  une  methode  trea 
simple  pour  decouvrir  a  40  millions  de  lieues  de  distance  la  nature  du 
soleil.  La  lumiere  proveuant  du  hard  de  cet  astre,  la  lumiere  emanee 
de  la  matiere  solaire  sous  un  angle  aigu,  et  nous  arrivant  sans  avoir 
eprouve  en  route  des  reflexions  ou  des  refractions  sensibles,  offre-t-elle 
des  traces  de  polarisation,  le  soleil  est  un  corps  solide  ou  liquide.  S'il 
n'y  a,  au  contraire,  aucun  indice  de  polarisation  dans  la  lumiere  du  bord, 
la  parte  incandescente  du  soleil  est  gazeuse.  C'est  par  cet  euchainement 
methodique  d'observations  qu'on  peut  arriver  a  des  notions  exactes  sur 
la  constitution  physique -du  soleil." 

"  By  the  aid  of  my  polariscope  I  discovered  (before  1820)  that  the 
light  of  all  terrestrial  objects  in  a  state  of  incandescence,  whether  they 
be  solid  or  liquid,  is  natural  as  long  as  it  emanates  from  the  object  in 
perpendicular  rays.  The  light  emanating  from  an  incandescent  surface 
at  an  acute  angle  presents,  on  the  other  hand,  manifest  proofs  of  polar- 
ization. I  will  not  pause  to  remind  you  that  this  circumstance  has  led 
me  to  the  remarkable  conclusion  that  light  is  not  generated  on  the  sur- 
face of  bodies  only,  but  that  some  portion  is  actually  engendered  within 
the  substance  itself,  even  in  the  case  of  platinum.  I  need  only  here  ob- 
serve, that  in  repeating  the  same  series  of  experiments  (aud  with  the 
same  instruments)  on  the  light  emanating  from  a  burning  gaseous  sub- 
stance, I  could  not  discover  any  characteristics  of  polarized  light,  what- 
ever might  be  the  angle  at  which  it  emanated  ;  and  I  found  that  the  light 
of  gaseous  bodies  is  natural  light  when  it  issues  from  the  burning  sur- 
face, although  this  circumstance  does  not  prevent  its  subsequent  com- 
plete polarization,  if  subjected  to  suitable  reflections  or  refractions. 
Hewoe  we  obtain  a  most  simple  method  of  discovering  the  nature  of  the 
sun  at  a  distance  of  40  millions  of  leagues.  For  if  the  light  emanating 
from  the  margin  of  the  sun,  and  radiating  from  the  solar  substance  at  an 
acute  angle,  reach  us  without  having  experienced  any  sensible  reflec- 
tions or  refractions  in  its  passage  to  the  earth,  and  if  it  offer  traces  of 
polarization,  the  sun  must  be  a  solid  or  a  liquid  body.  Put  if,  on  the 
contrary,  the  light  emanating  from  tke  sun's  margin  giv-  no  indications 
of  polarization,  the  incandescent  portion  of  the  sun  inuetbe  %a»euu».  it 


POLARIZATION    OF    LIGHT.  47 

mospheric  strata,  and  even  the  smallest  amount  of  water  they 
contain,  of  scrutinizing  the  depths  of  the  ocean  and  its  rocks 
by  means  of  a  tourmaline  plate,*  and,  in  accordance  with 
Newton's  prediction,  of  comparing  the  chemical  compositionf 
of  several  substances^  with  their  optical  effects.  It  will  be 
sufficient  to  mention  the  names  of  Airy,  Arago,  Biot,  Brew- 
ster,  Cauchy,  Faraday,  Fresnel,  John  Herschel,  Lloyd,  Ma- 
lus,  Neumann,  Plateau,  Seebeck, to  remind  the  sci- 
entific reader  of  a  succession  of  splendid  discoveries  and  of 
their  happy  applications.  The  great  and  intellectual  labors 
of  Thomas  Young  more  than  prepared  the  way  for  these  im- 
portant efforts.  Arago's  polariscope  and  the  observation  of 
the  position  of  colored  fringes  of  diffraction  (in  consequence 
of  interference)  have  been  extensively  employed  in  the  pros- 
ecution of  scientific  inquiry.  Meteorology  has  made  equal 
advances  with  physical  astronomy  in  this  new  path. 

However  diversified  the  power  of  vision  may  be  in  differ- 
ent persons,  there  is  nevertheless  a  certain  average  of  organ- 
is  by  means  of  such  a  methodical  sequence  of  observations  that  we  may 
acquire  exact  ideas  regarding  the  physical  constitution  of  the  sun." 
(On  the  Envelopes  of  the  Sun,  see  Arago,  in  the  Annuaire  pour  1846, 
p.  464.)  I  give  all  the  circumstantial  optical  disquisitions  •which  I  have 
borrowed  from  the  manuscript  or  printed  works  of  my  friend,  in  his 
own  words,  in  order  to  avoid  the  misconceptions  to  which  the  variations 
of  scientific  terminology  might  give  rise  in  retranslating  the  passages 
into  French,  or  any  other  of  the  various  languages  in  which  the  Cosmos 
has  appeared. 

*  "  Sur  1'effet  d'une  lame  de  tourmaline  taillee  parallelement  aux 
aretes  du  prisme  servant,  lorsqu'elle  est  convenablement  situee,  a  61i- 
miner  en  totalite  les  rayons  reflechis  par  la  surface  de  la  mer  et  meles  £ 
la  lumiere  provenant  de  1'ecueil."  "  On  the  effect  of  a  tourmaline  plate 
cut  parallel  to  the  edges  of  the  prism,  in  concentrating  (when  placed  in 
a  suitable  position)  all  the  rays  of  light  reflected  by  the  surface  of  the 
sea,  and  blended  with  the  light  emanating  from  the  sunken  rocks." 
See  Arago,  Instructions  de  la  Bonite,  in  the  Annuaire  pour  1836,  p.  339 

343. 

t  "  De  la  possibilit6  de  d6terminer  les  pouvoirs  refringents  des  corps 
d'apres  leur  composition  chimique."  On  the  possibility  of  determining 
the  refracting  powers  of  bodies  according  to  their  chemical  composition 

applied  to  the  ratio  of  the  oxygen  to  the  nitrogen  in  atmospheric  air, 
to  the  quantity  of  hydrogen  contained  in  ammonia  and  in  water,  to  car- 
bonic acid,  alcohol,  and  the  diamond).  See  Biot  ct  Arago,  Mtmoire 
sur  les  Ajfinites  des  Corps  pour  la  Lumiere,  Mars,  1806;  also  Mlmoirts 
Mathem.  et  Phys.  de  V Inslilut,  t.  vii.,  p.  327-346 ;  and  my  M6moire  gur 
les  Refractions  Astronomiques  dans  la  Zone  Torride,  in  the  Recueit 
d'Obsew.  Astron.,  vol.  i.,  p.  115  and  122. 

t  Experiences  de  M.  Arago  sur  la  puissance  Refractive  des  Corps  D\- 
aphanes  (de  I' air  sec  ct  de  I' air  humide)  par  le  Replacement  des  Franges, 
iu  Moigno,  Repertoire  d'Oplique  Mod.,  1847,  p.  159-K52. 


48  COSMOS. 

fc  capacity,  which  was  the  same  among  former  generation!, 
as,  for  instance,  the  Greeks  and  Romans,  as  at  the  present 
day.  The  Pleiades  prove  that  several  thousand  years  ago, 
even  as  now,  stars  which  astronomers  regard  as  of  the  sev- 
enth magnitude,  wera  invisible  to  the  naked  eye  of  average 
visual  power.  The  group  of  the  Pleiades  consists  of  one 
star  of  the  third  magnitude,  Alcyone  ;  of  two  of  the  fourth, 
Electra  and  Atlas  ;  of  three  of  the  fifth,  Merope,  Maia,  and 
Taygeta  ;  of  two  hetween  the  sixth  and  the  seventh  magni- 
tudes, Pleione  and  Celseno  ;  of  one  between  the  seventh  and 
the  eighth,  Asterope  ;  and  of  many  very  minute  telescopic 
stars.  I  make  use  of  the  nomenclature  and  order  of  succes 
sion  at  present  adopted,  as  the  same  names  were  among  the 
ancients  in  part  applied  to  other  stars.  The  six  first-named 
stars  of  the  third,  fourth,  and  fifth  magnitudes  were  the  only 
ones  which  could  be  readily  distinguished.*  Of  these  Ovid 
says  (Fast.,  iv.,  170), 

"  Qua;  septem  dici,  sex  tamen  esse  solent." 

One  of  the  daughters  of  Atlas,  Merope,  the  only  one  who 
was  wedded  to  a  mortal,  was  said  to  have  veiled  herself  for 
very  shame,  or  even  to  have  wholly  disappeared.  This  is 
probably  the  star  of  about  the  seventh  magnitude,  which  we 
call  Celajno  ;  for  Hipparchus,  in  his  commentary  on  Aratus, 
observes  that  on  clear  moonless  nights  seven  stars  may  ac- 
tually be  seen.  Celseno,  therefore,  must  have  been  seen,  for 
Pleione,  which  is  of  equal  brightness,  is  too  near  to  Atlas,  a 
star  of  the  fourth  magnitude. 

The  little  star  Alcor,  which,  according  to  Triesnecker,  is 
situated  in  the  tail  of  the  Great  Bear,  at  a  distance  of  11' 

*  Hipparchus  says  (ad  Arati  Phcen.,  1,  p.  190,  in  Uranologio  Pctavii), 
in  refutation  of  the  assertion  of  Aratus  that  there  were  only  six  stars 
visible  in  the  Pleiades :  "  One  star  escaped  the  attention  of  Aratus.  For 
when  the  eye  is  attentively  fixed  on  this  constellation  on  a  serene  and 
moonless  night,  seven  stars  are  visible,  and  it  therefore  seems  strange 
that  Attains,  in  his  description  of  the  Pleiades,  should  have  neglected 
to  notice  this  oversight  on  the  part  of  Aratus,  as  though  he  regarded  the 
statement  as  correct."  Merope  is  called  the  invisible  (•nava<j>avjjf')  in 
the  Catasterisms  (XXIII.)  ascribed  to  Eratosthenes.  On  a  supposed 
connection  between  the  name  of  the  veiled  (the  daughter  of  Atlas)  with 
the  geographical  myths  in  the  Meropis  of  Theopompus,  as  well  as  with 
the  great  Saturnian  Continent  of  Plutarch  and  the  Atlantis,  see  my  Ex 
amen  Grit,  de  VHist.  de  la  Geographic,  t.  i.,  p.  170.  Compare  also  Ideler 
Untersuchungen  fiber  den  Ursprung  imd  die  Bedeutung  der  Sternnamen, 
1809,  p.  145;  and  in  reference  to  astronomical  determination  of  place, 
consult  Madler,  Unttrsucli.  ubet  die  Fixstern-Systeme,  th.  ii.,  1848,  s.  38 
and  166 ;  also  Baily  in  the  Mem.  of  the  Astr.  Soc.,  vol.  xiii.,  p.  33. 


VISIBILITY    OF    STARS.  49 

48  from  Mizar,  is,  according  to  Argelander,  of  the  fifth 
magnitude,  but  overpowered  by  the  rays  of  Mizar.  It  was 
called  by  the  Arabs  Saidak,  "  the  Test,"  because,  as  the  Per- 
sian astronomer  Kazwini*  remarks,  "  It  was  employed  as  a 

*  See  Ideler,  Sternnamen,  s.  19  and  25.  Arago,  in  manuscript  notices 
of  the  year  1847,  writes  as  follows:  " On  observe  qu'une  lumiere  forte 
fait  disparaltre  une  lumiere  faible  placee  dans  le  voisinage.  Quelle 
peut  en  etre  la  cause  ?  II  est  possible  physiologiquement  que  1'ebran- 
lement communique  k  la  retine  par  la  lumiere  forte  s'etend  au  del&  des 
points  que  la  lumiere  forte  a  frappes,  et  que  cet  ebranlement  secon- 
daire  absorbe  et  neutralise  en  quelque  sorte  1'ebranlement  provenant  de 
la  seconde  et  faible  lumiere.  Mais  sans  entrer  dans  ces  causes  physio- 
logiques,  il  y  a  une  cause  directe  qu'on  peut  indiquer  pour  la  dispari- 
tion  de  la  faible  lumiere :  c'est  que  les  rayons  provenant  de  la  grande 
n'ont  pas  seulement  forme  une  image  nette  sur  la  retine,  mais  se  sont 
disperses  aussi  sur  toutes  les  parties  de  cet  organe  £  cause  des  imper- 
fections de  transparence  de  la  cornee.  Les  rayons  du  corps  plus  bril- 
lant  a  en  traversant  la  cornee  se  comportent  comme  en  traversant  un 
corps  legerement  depoli.  Une  partie  des  ces  rayons  refractes  reguliere- 
ment  forme  1'image  neme  de  a,  1'autre  partie  disperses  eclaire  la  totalite 
de  la  retine.  C'est  done  sur  ce  fond  lumineux  que  se  projette  1'image 
de  1'objet  voisin  b.  Cette  derniere  image  doit  done  ou  disparaltre  ou 
etre  affaiblie.  De  jour  deux  causes  contribuent  £  1'affaiblissement  des 
etoiles.  L'une  de  ces  causes  c'est  1'image  distincte  de  cette  portion  de 
ratmosphere  comprise  dans  la  direction  de  1'etoile  (de  la  portion  aeri- 
enne  placee  entre  1'oeil  et  1'etoile)  et  sur  laquelle  1'image  de  1'etoile  vient 
de  se  peindre ;  1'autre  cause  c'est  la  lumiere  diffuse  provenant  de  la  dis- 
persion que  les  defauts  de  la  cornee  imprlment  aux  rayons  emanants  de 
tous  les  points  de  1'atmosphere  visible.  De  nuit  les  couches  atmosphe- 
riques  interposees  entre  1'oeil  et  1'etoile  vers  laquelle  on  vise,  n'agissent 
pas ;  chaque  etoile  du  firmament  forme  une  image  plus  nette,  mais  une 
partie  de  leur  lumiere  se  trouve  dispersee  a,  cause  du  manque  de  dia- 
phanite  de  la  cornee.  Le  me  me  raisonnement  s'applique  4  une  deux- 
icme,  troisieme  ....  millidme  etoile.  La  retine  se  trouve  done  eclai- 
ree  en  totalite  par  une  lumiere  diffuse,  proportionnelle  au  nombre  de 
ces  etoiles  et  a  leur  eclat.  On  con^oit  par  1&  que  cette  somme  de  lu- 
miere diffuse  affaiblisse  ou  fasse  entierement  disparaitre  1'image  do 
1'etoile  vers  laquelle  on  dirige  la  vue." 

"  We  find  that  a  strong  light  causes  a  fainter  one  placed  near  it  to  dis- 
appear. What  can  be  the  cause  of  this  phenomenon  ?  It  is  physiolog- 
ically possible  that  the  vibration  communicated  to  the  retina  by  strong 
light  may  extend  beyond  the  points  excited  by  it;  and  that  this  secondary 
vioration  may  in  some  degree  absorb  and  neutralize  that  arising  from  the 
second  feeble  light.  Without,  however,  entering  upon  these  physiologic- 
al considerations,  there  is  a  direct  cause  to  which  we  may  refer  the  disap- 
pearance of  the  feeble  light,  viz.,  that  the  rays  emanating  from  the  strong 
light,  after  forming  a  perfect  image  on  the  retina,  are  dispersed  over  all 
parts  of  this  organ  in  consequence  of  the  imperfect  transparency  of  the 
cornea.  The  rays  of  the  more  brilliant  body  a,  in  passing  the  cornea, 
are  affected  in  th.2  same  manner  as  if  they  were  transmitted  through  a 
body  whose  surface  was  not  perfectly  smooth.  Some  of  these  regularly 
refracted  rays  form  the  image  a,  while  the  remainder  of  the  dispersed 
rays  illumine  the  whole  jf  the  retina.  On  this  luminous  ground  the 
VOL.  III.— C 


60  COSMOS. 

test  of  the  power  of  vision."  Notwithstanding  the  low  po- 
sition of  the  Great  Bear  under  the  tropics,  I  have  very  dis- 
tinctly seen  Alcor,  evening  after  evening,  with  the  naked 
eye,  on  the  rainless  shores  of  Cumana,  and  on  the  plateaux 
of  the  Cordilleras,  which  are  elevated  nearly  13,000  feet 
above  the  level  of  the  sea,  while  I  have  seen  it  less  frequent- 
ly and  less  distinctly  in  Europe  and  in  the  dry  atmosphere 
of  the  Steppes  of  Northern  Asia.  The  limits  within  which 
the  naked  eye  is  unable  to  separate  two  very  contiguous  ob- 
jects in  the  heavens  depend,  as  Madler  has  justly  observed, 
on  the  relative  brilliancy  of  the  stars.  The  two  stars  of  the 
third  and  fourth  magnitudes,  marked  as  a  Capricorni,  which 
are  distant  from  each  other  six  and  a  half  minutes,  can  with 
ease  be  recognized  as  separate.  Galle  thinks  that  £  and  6 
Lyrse,  being  both  stars  of  the  fourth  magnitude,  may  be  dis- 
tinguished in  a  very  clear  atmosphere  by  the  naked  eye,  al- 
though situated  at  a  distance  of  only  three  and  a  half  min- 
utes from  each  other. 

The  preponderating  effect  of  the  rays  of  the  neighboring 
planet  is  also  the  principal  cause  of  Jupiter's  satellites  re- 
maining invisible  to  the  naked  eye  ;  they  are  not  all,  how- 
ever, as  has  frequently  been  maintained,  equal  in  brightness 
to  stars  of  the  fifth  magnitude.  My  friend,  Dr.  Galle,  has 
found  from  recent  estimates,  and  by  a  comparison  with 
neighboring  stars,  that  the  third  and  brightest  satellite  is 
probably  of  the  fifth  or  sixth  magnitude,  while  the  others, 
which  are  of  various  degrees  of  brightness,  are  all  of  the  sixth 
or  seventh  magnitude.  There  are  only  few  cases  on  record 
in  which  persons  of  extraordinarily  acute  vision — that  is  to 
say,  capable  of  clearly  distinguishing  with  the  naked  eye 


image  of  the  neighboring  object  b  is  projected.  This  last  imago  must 
therefore  either  wholly  disappear  or  be  dimmed.  By  day  two  causes 
contribute  to  weaken  the  light  of  the  stars ;  one  is  the  distinct  image 


of  that  portion  of  the  atmosphere  included  in  the  direction  of  the  star 
(the  aerial  field  interposed  between  the  eye  and  the  star),  and  on  which 
the  image  of  the  star  is  formed,  while  the  other  is  the  light  diffused  by 
the  dispersion  which  the  defects  of  the  cornea  impress  on  the  rays  em- 
anating from  all  points  of  the  visible  atmosphere.  At  night,  the  strata 
of  air  interposed  between  the  eye  and  the  star  to  which  we  direct  the 
instrument,  exert  no  disturbing  action ;  each  star  in  the  firmament  forms 
a  more  perfect  image,  but  a  portion  of  the  light  of  the  stars  is  dispered 
in  consequence  of  the  imperfect  transparency  of  the  cornea.  The  same 
reasoning  applies  to  a  second,  a  third,  or  a  thousandth  star.  The  retina, 
then,  is  entirely  illumined  by  a  diffused  light,  proportionate  to  the  num- 
ber of  the  stars  and  to  their  brilliancy.  Hence  we  may  imagine  that 
the  aggregate  of  this  diffused  light  must  either  weaken,  or  entirely  ob- 
literate the  imago  of  tlie  star  toward  which  the  eye  is  directed." 


VISIBILITY    OF    STARS.  51 

gtars  fainter  than  those  of  the  sixth  magnitude — have  been 
able  to  distinguish  the  satellites  of  Jupiter  without  a  tele- 
scope. The  angular  distance  of  the  third  and  brightest  sat- 
ellite from  the  center  of  the  planet  is  4'  42"  ;  that  of  the 
fourth,  which  is  only  one  sixth  smaller  than  the  largest,  is 
8'  16"  ;  and  all  Jupiter's  satellites  sometimes  exhibit,  as  Ar- 
ago  maintains,*  a  more  intense  light  for  equal  surfaces  than 

*  Arago,  in  the  Annuaire  pour  1842,  p.  284,  and  in  the  Compte* 
Rendus,  torn,  xv.,  1842,  p.  750.  (Schutn.,  Astron.  Nachr.,  No.  702.) 
"  I  have  instituted  some  calculations  of  magnitudes,  in  reference  to  your 
conjectures  on  the  visibility  of  Jupiter's  satellites,"  writes  Dr.  Galle,  in 
letters  addressed  to  me,  "  but  I  have  found,  contrary  to  my  expecta- 
tions, that  they  are  not  of  the  fifth  magnitude,  but,  at  most,  only  of  the 
sixth,  or  even  of  the  seventh  magnitude.  The  third  and  brightest  sat- 
ellite alone  appeared  nearly  equal  in  brightness  to  a  neighboring  star 
of  the  sixth  magnitude,  which  I  could  scarcely  recognize  with  the  naked 
eye,  even  at  some  distance  from  Jupiter ;  so  that,  considered  in  refer- 
ence to  the  brightness  of  Jupiter,  this  satellite  would  probably  be  of  the 
fifth  or  sixth  magnitude  if  it  were  isolated  from  the  planet.  The  fourth 
satellite  was  at  its  greatest  elongation,  but  yet  I  could  not  estimate  it  at 
more  than  the  seventh  magnitude.  The  rays  of  Jupiter  would  not  pre- 
vent this  satellite  from  being  seen  if  it  were  itself  brighter.  From  a 
comparison  of  Aldebaran  \vith  the  neighboring  star  6  Tauri,  which  is 
easily  recognized  as  a  double  star  (at  a  distance  of  5J  minutes),  I  should 
estimate  the  radiation  of  Jupit«r  at  five  or  six  minutes,  at  least,  for  or- 
dinary vision."  These  estimates  correspond  with  those  of  Arago,  who 
is  even  of  opinion  that  this  false  radiation  may  amount  in  the  case  of 
some  persons  to  double  this  quantity.  The  mean  distances  of  the  four 
satellites  from  the  center  of  the  main  planet  are  undoubtedly  1'  51", 
2'  57",  4'  42",  and  8'  16".  "  Si  nous  supposons  que  1'image  de  Jupiter, 
dans  certains  yeux  exceptionnels,  s'epanouisse  seulement  par  des  ray- 
ons d'une  ou  deux  minutes  d'amplitude,  il  ne  semblera  pas  impossible 
que  les  satellites  soient  de  terns  en  terns  aper9us,  sans  avoir  besoin  de 
recourir  a  1'artifice  de  1'amplification.  Pour  verifier  cette  conjecture, 
j'ai  fait  construire  une  petite  lunette  dans  laquelle  1'objectif  et  1'ocu- 
laire  ont  a  peu  pres  le  menie  foyer,  et  qni  des  lors  lie  grossit  point. 
Cette  lunette  ne  detruit  pas  eutierement  les  rayons  divergents,  mais 
elle  en  reduit  considerablement  la  longueur.  Cela  a  suffi  your  qu'un 
satellite  convenablement  6cart6  de  la  plandte,  soil  devenu  visible.  Le 
fait  a  ete  constate  par  tous  les  jeunes  astronomes  de  1'Observatoire." 
"  If  we  suppose  that  the  image  of  Jupiter  appears  to  the  eyes  of  some 
persons  to  be  dilated  by  rays  of  only  one  or  two  minutes,  it  is  nit  im- 
possible that  the  satellites  may  from  time  to  time  be  seen  without  the 
aid  of  magnifying  glasses.  In  order  to  verify  this  conjecture,  I  caased 
a  small  instrument  to  be  constructed  in  which  the  object-glass  and  the 
eye-piece  had  nearly  the  same  focus,  and  which,  therefore,  did  not  mag 
itify.  This  instrument  does  not  entirely  destroy  the  diverging  rays,  al 
though  it  considerably  reduces  their  length.  This  method  has  sufficed 
to  render  a  satellite  visible  'when  at  a  sufficient  distance  from  the  planet. 
This  observation  has  been  confirmed  by  all  the  young  astronomers  at 
the  Observatory."  (Arago,  in  the  Comptes  Rendus,  torn,  xv.,  1842,  p. 


52  COSMOS. 

Jupiter  himself;  occasionally,  however,  as  shown  by  recent 
observations,  they  appear  like  gray  spots  on  the  planet.  The 
rays  or  tails,  which  to  our  eyes  appear  to  radiate  from  the 
planets  and  fixed  stars,  and  which  were  used,  since  the  ear- 
liest ages  of  mankind,  and  especially  among  the  Egyptians, 
as  pictorial  representations  to  indicate  the  shining  orbs  of 
heaven,  are  at  least  from  five  to  six  minutes  in  length. 
(These  lines  are  regarded  by  Hassenfratz  as  caustics  on  the 
crystalline  lens  :  intersections  des  deux  caustiques.} 

"  The  image  of  the  star  which  we  see  with  the  naked  eye 
is  magnified  by  diverging  rays,  in  consequence  of  which  it 
occupies  a  larger  space  on  the  retina  than  if  it  were  concen- 

As  a  remakable  instance  of  acute  vision,  and  of  the  great  sensibility 
of  the  retina  in  some  individuals  who  are  able  to  see  Jupiter's  satellites 
with  the  naked  eye,  I  may  instance  the  case  of  a  master  tailor,  named 
Schbn,  who  died  at  Breslau  in  1837,  and  with  reference  to  whom  I  have 
received  some  interesting  communications  from  the  learned  and  active 
director  of  the  Breslau  Observatory,  Von  Boguslawski.  "  After  having 
(since  1820)  convinced  ourselves,  by  several  rigid  tests,  that  in  serene 
moonless  nights  Schbn  was  able  correctly  to  indicate  the  position  of  sev- 
eral of  Jupiter's  satellites  at  the  same  time,  we  spoke  to  him  of  the  em- 
anations and  tails  which  appeared  to  prevent  others  from  seeing  so 
clearly  as  he  did,  when  he  expressed  his  astonishment  at  these  ob- 
structing radiations.  From  the  animated  discussions  between  himself 
and  the  by-standers  regarding  the  difficulty  of  seeing  the  satellites  with 
the  naked  eye,  the  conclusion  was  obvious,  that  the  planet  and  fixed 
stars  must  always  appear  to  Schbii  like  luminous  points  having  no  rays. 
He  saw  the  third  satellite  the  best,  and  the  first  very  plainly  when  it 
was  at  the  greatest  digression,  but  he  never  saw  the  second  and  the 
fourth  alone.  When  the  air  was  not  in  a  very  favorable  condition,  the 
satellites  appeared  to  him  like  faint  streaks  of  light.  He  never  mistook 
small  fixed  stars  for  satellites,  probably  on  account  of  the  scintillating 
and  less  constant  light  of  the  former.  Some  years  before  his  death 
Schbn  complained  to  me  that  his  failing  eye  could  no  longer  distinguish 
Jupiter's  satellites,  whose  position  was  only  indicated,  even  in  clear 
weather,  by  light  faint  streaks."  These  circumstances  entirely  coin- 
cide with  what  has  been  long  known  regarding  the  relative  luster  of 
Jupiter's  satellites,  for  the  brightness  and  quality  of  the  light  probably 
exert  a  greater  influence  than  mere  distance  from  the  main  planet  on 
persons  of  such  great  perfection  and  sensibility  of  vision.  Schbii  never 
saw  the  second  nor  the  fourth  satellite.  The  former  is  the  smallest  of 
all ;  the  latter,  although  the  largest  after  the  third  and  the  most  remote, 
is  periodically  obscured  by  a  dark  color,  and  is  generally  the  faintest 
of  all  the  satellites.  Of  the  third  and  the  first,  which  were  best  and 
most  frequently  seen  by  the  naked  eye,  the  former,  which  is  the  largest 
of  all,  is  usually  the  brightest,  and  of  a  very  decided  yellow  color ;  the 
latter  occasionally  exceeds  in  the  intensity  of  its  clear  yellow  light  the 
luster  of  the  third,  which  is  also  much  larger.  (Madler,  Astr.,  1846, 
s.  231-234,  and  439.)  Sturm  and  Airy,  in  the  Complex  Rendut,  t.  xx., 
p.  764-6,  show  how,  under  proper  conditions  of  refraction  in  the  organ 
of  vision,  remote  luminous  poin'a  may  appear  as  light  streaks. 


NATURAL   VISION.  53 

trated  in  a  single  point.  The  impression  on  the  nerves  is 
weaker.  A  very  dense  starry  swarm,  in  which  scarcely  any 
of  the  separate  stars  belong  even  to  the  seventh  magnitude, 
may,  on  the  contrary,  be  visible  to  the  unaided  eye  in  con- 
sequence of  the  images  of  the  many  different  stars  crossing 
each  other  upon  the  retina,  by  which  every  sensible  point  of 
its  surface  is  more  powerfully  excited,  as  if  by  one  concen- 
trated image."* 

*  "  L'image  fpanouie  d'ane  etoile  de  7eme  grandeur  n'ebranle  pas 
suffisamment  la  retine :  elle  n'y  fait  pas  naitre  une  sensation  apprecia- 
ole  de  lumiere.  Si  1'image  n'etait  point  epanouie  (par  des  rayons  di- 
vergents),  la  sensation  aurait  plus  de  force,  et  1'etoile  se  verrait.  La 
premiere  classe  d'etoiles  invisibles  a  1'ceil  nu  ne  serait  plus  alors  la  sep- 
tieme:  pour  la  trouver,  il  faudrait  peut-etre  descendre  alors  jusqu'a  la 
12etne.  Considerons  un  groupe  d'etoiles  de  7eme  grandeur  tellement 
rapproch6es  les  unes  des  autres  que  les  intervalles  echappent  necessaire- 
ment  a  1'oeil.  Si  la  vision  avait  de  la  nettete,  si  1'image  de  chaque  etoile 
etait  tres  petite  et  bien  termin&e,  1'observateur  aperceverait  un  champ 
de  lumiere  dont  chaque  point  aurait  Veclat  concentre  d'une  etoile  de 
7eme  grandeur.  I? eclat  concentre  d'une  etoile  de  7eme  grandeur  suffit 
a  la  vision  a  1'oeil  nu.  Le  groupe  serait  done  visible  a  I'ojil  nu.  Di- 
latons  maintenant  sur  la  retine  1'image  de  chaque  etoile  du  groupe ; 
remplasons  chaque  point  de  1'ancienne  image  generale  par  un  petit  cer- 
cle :  ces  cercles  empieteront  les  uns  sur  les  autres,  et  les  divers  points 
de  la  retine  se  trouveront  eclaires  par  de  la  lumiere  venaut  simultan  - 
ment  de  plusieurs  etoiles.  Pour  peu  qu'on  y  reflechisse,  il  restera  evi- 
dent qu'  excepte  sur  les  bords  de  1'image  g6nerale,  1'aire  lumineuse 
ainsi  eclairee  a  precisement,  a  cause  de  la  superposition  des  cercles,  la 
m£me  inteusite  que  dans  le  cas  ou  chaque  etoile  n'eclaire  qu'un  seul 
point  au  fond  de  1'ceil ;  mais  si  chacun  de  ces  points  re<joit  une  lumiere 
6gale  en  intensity  a  la  lumiere  concentree  d'une  etoile  de  7eme  gran- 
deur, il  est  clair  que  1'epanouissement  des  images  individuelles  des 
fetoiles  contigues  ne  doit  pas  empecher  la  visibilite  de  1'ensemble.  Les 
instruments  telescopiques  ont,  quoiqu'a  un  beaucoup  momdre  degre,  le 
defaut  de  donner  aussi  aux  etoiles  un  diamitre  sensible  et  factice.  Avec 
ces  instruments,  comme  &  1'ceil  nu,  on  doit  done  apercevoir  des  groupes, 
composes  d'etoiles  inferieures  en  intensite  a  celles  que  les  memea  lu- 
nettes ou  telescopes  feraient  apercevoir  isolement." 

"  The  expanded  image  of  a  star  of  the  seventh  magnitude  doen  not 
cause  sufficient  vibration  of  the  retina,  and  does  not  give  rise  to  an  ap- 
preciable sensation  of  light.  If  the  image  were  not  expanded  (by  di- 
vergent rays),  the  sensation  would  be  stronger  and  the  star  discernible. 
The  lowest  magnitude  at  which  stars  are  visible  would  not  therefore 
be  the  seventh,  but  some  magnitude  as  low  perhaps  as  the  twelfth  de- 
gree. Let  us  consider  a  group  of  stars  of  the  seventh  magnitude  so 
close  to  one  another  that  the  intervals  between  them  necessarily  escape 
the  eye.  If  the  sight  were  very  clear,  and  the  image  of  each  star  small 
and  well  defined,  the  observer  would  perceive  a  field  of  light,  each 
point  of  which  would  be  equal  to  the  concentrated  brightness  of  a  star 
of  the  seventh  magnitude.  The  concentrated  light  of  a  star  of  the  sev- 
enth magnitude  is  sufficient  to  be  seen  by  the  naked  eye.  The  group, 
therefore,  would  be  visible  to  the  naked  eye.  Let  us  now  dilate  the 


54  COSMOS. 

Telescopes,  although  in  a  much  less  degree,  unfortunately 
also  give  the  stars  an  incorrect  and  spurious  diameter  ;  but, 
according  to  the  splendid  investigations  of  Sir  William  Her- 
echel,*  these  diameters  decrease  with  the  increasing  power 
of  the  instrument.  This  distinguished  observer  estimated 
that,  at  the  excessive  magnifying  power  of  6500,  the  appar- 
ent diameter  of  Vega  Lyrae  still  amounted  to  0"36.  In  ter- 
restrial objects,  the  form,  no  less  than  the  mode  of  illumina- 
tion, determines  the  magnitude  of  the  smallest  angle  of  vision 
for  the  naked  eye.  Adams  very  correctly  observed  that  a 
long  and  slender  staff  can  be  seen  at  a  much  greater  distance 
than  a  square  whose  sides  are  equal  to  the  diameter  of  the 
staff.  A  stripe  may  be  distinguished  at  a  greater  distance 
than  a  spot,  even  when  both  are  of  the  same  diameter.  Ara- 
go  has  made  numerous  calculations  on  the  influence  of  form 
(outline  of  the  object)  by  means  of  angular  measurement  of 
distant  lightning  conductors  visible  from  the  Paris  Observa- 
tory. The  minimum  optical  visual  angle  at  which  terres- 
trial objects  can  be  recognized  by  the  naked  eye  has  been 
gradually  estimated  lower  and  lower  from  the  time  when 
Robert  Hooke  fixed  it  exactly  at  a  full  minute,  and  Tobias 
Mayer  required  34"  to  perceive  a  black  speck  on  white  pa- 
per, to  the  period  of  Leeuwenhoek's  experiments  with  spi- 
der's threads,  which  are  visible  to  ordinary  sight  at  an  angle 
of  4"-7.  In  the  recent  and  most  accurate  experiments  of 
Hueck,  on  the  problem  of  the  movement  of  the  crystalline 

image  of  each  star  of  the  group  on  the  retina,  and  substitute  a  small 
circle  for  each  point  of  the  former  general  image ;  these  circles  will 
impinge  upon  one  another,  and  the  different  points  of  the  retina  will 
be  illumined  by  light  emanating  simultaneously  from  many  stars.  A 
slight  consideration  will  show,  that,  excepting  at  the  margins  of  the 
general  image,  the  luminous  air  has,  in  consequence  of  the  superposi- 
tion of  the  circles,  the  same  degree  of  intensity  as  in  those  cases  where 
each  star  illumines  only  one  single  point  of  the  retina ;  but  if  each  of 
these  points  be  illumined  by  a  light  equal  in  intensity  to  the  concen- 
trated light  of  a  star  of  the  seventh  magnitude,  it  is  evident  that  the 
dilatation  of  the  individual  images  of  contiguous  stars  can  not  prevent 
the  visibility  of  the  whole.  Telescopic  instruments  have  the  defect, 
although  in  a  much  less  degree,  of  giving  the  stars  a  sensible  and  spu. 
rious  diameter.  We  therefore  perceive  with  instruments,  no  less  than 
with  the  naked  eye,  groups  of  stars,  inferior  in  intensity  to  those  which 
the  same  telescopic  or  natural  sight  would  recognize  if  they  were  iso- 
lated."— Arago,  in  the  Annuaire  du  Bureau  des  Longitudes  pour  Van 
1842,  p.  284. 

*  Sir  William  Herschel,  in  the  Philos.  Transact,  for  1803,  vol.  93, 
p.  "225,  and  for  1805,  vol.  94,  p.  184.  Compare  also  Arago,  in  the  An 
nuairepour  1842,  p.  360-374. 


VISIBILITY    OP   OBJECTS.  55 

lens,  white  lines  on  a  black  ground  were  seen  at  an  angle 
of  l"-2;  a  spider's  thread  at  0"-6  ;  and  a  fine  glistening 
wire  at  scarcely  0"'2.  This  problem  does  not  admit  gen- 
erally of  a  numerical  solution,  since  it  entirely  depends  on 
the  form  of  the  objects,  their  illumination,  their  contrast  with 
the  back-ground,  and  on  the  motion  or  rest,  and  the  nature 
of  the  atmospheric  strata  in  which  the  observer  is  placed. 

During  my  visit  at  a  charming  country-seat  belonging  to 
the  Marquess  de  Selvalegre  at  Chillo,  not  far  from  Q,uito, 
where  the  long-extended  crests  of  the  volcano  of  Pichincha 
lay  stretched  before  me  at  a  horizontal  distance,  trigonomet- 
rically  determined  at  more  than  90,000  feet,  I  was  much 
struck  by  the  circumstance  that  the  Indians  who  were  stand- 
ing near  me  distinguished  the  figure  of  my  traveling  com- 
panion Bonpland  (who  was  engaged  in  an  expedition  to  the 
volcano)  as  a  white  point  moving  on  the  black  basaltic  sides 
of  the  rock,  sooner  than  we  could  discover  him  with  our  tel- 
escopes. The  white  moving  image  was  soon  detected  with 
the  naked  eye  both  by  myself  and  by  my  friend  the  unfor- 
tunate son  of  the  marquess,  Carlos  Montufar,  who  subsequent- 
ly perished  in  the  civil  war.  Bonpland  was  enveloped  in  a 
white  cotton  mantle,  the  poncho  of  the  country  ;  assuming 
the  breadth  across  the  shoulders  to  vary  from  three  to  five 
feet,  according  as  the  mantle  clung  to  the  figure  or  fluttered 
in  the  breeze,  and  judging  from  the  known  distance,  we  found 
that  the  angle  at  which  the  moving  object  could  be  distinctly 
seen  varied  from  7"  to  12".  White  objects  on  a  black  ground 
are,  according  to  Hueck's  repeated  experiments,  distinguish- 
ed at  a  greater  distance  than  black  objects  on  a  white  ground. 
The  light  was  transmitted  in  serene  weather  through  rar- 
efied strata  of  air  at  an  elevation  15,360  feet  above  the 
level  of  the  sea  to  our  station  at  Chillo,  which  was  itself  sit- 
uated at  an  elevation  of  8575  feet.  The  ascending  distance 
was  91,225  feet,  or  about  17£  miles.  The  barometer  and 
thermometer  stood  at  very  different  heights  at  both  stations, 
being  probably  at  the  upper  one  about  17*2  inches  and  46°'4, 
while  at  the  lower  station  they  were  found,  by  accurate  ob- 
servation, to  be  22-2  inches  and  65°-7.  Gauss's  heliotrope 
light,  which  has  become  so  important  an  element  in  German 
trigonometrical  measurements,  has  been  seen  with  the  naked 
eye  reflected  from  the  Brocken  on  Hohenhagen,  at  a  distance 
of  about  227,000  feet,  or  more  than  42  miles,  being  fre- 
quently visible  at  points  in  which  the  apparent  breadth  of  a 
three-inch  mirror  was  only  0"'43. 


56  COSMOS. 

The  visibility  of  distant  objects  irf  modified  by  the  absorp- 
tion of  the  rays  passing  from  the  terrestrial  object  to  the* 
naked  eye  at  unequal  distances,  and  through  strata  of  air 
more  or  less  rarefied  and  more  or  less  saturated  with  moist- 
ure ;  by  the  degree  of  intensity  of  the  light  diffused  by  the 
radiation  of  the  particles  of  air ;  and  by  numerous  meteoro- 
logical processes  not  yet  fully  explained.  It  appears  from 
the  old  experiments  of  the  accurate  observer  Bouguer  that 
a  difference  of  ^th  in  the  intensity  of  the  light  is  necessary 
to  render  objects  visible.  To  use  his  own  expression,  we 
only  negatively  see  mountain-tops  from  which  but  little  light 
is  radiated,  and  which  stand  out  from  the  vault  of  heaven  in 
the  form  of  dark  masses ;  their  visibility  is  solely  owing  to 
the  difference  in  the  thickness  of  the  atmospheric  strata  ex- 
tending respectively  to  the  object  and  to  the  horizon.  Strong 
ly-illumined  objects,  such  as  snow-clad  mountains,  white 
chalk  cliffs,  and  conical  rocks  of  pumice-stone,  are  seen  pos- 
itively. 

The  distance  at  which  high  mountain  summits  may  be 
recognized  from  the  sea  is  not  devoid  of  interest  in  relation 
to  practical  navigation,  where  exact  astronomical  determina- 
tions are  wanting  to  indicate  the  ship's  place.  I  have  treat- 
ed this  subject  more  at  length  in  another  work,*  where  I 
considered  the  distance  at  which  the  Peak  of  Teneriffe  might 
be  seen. 

The  question  whether  stars  can  be  seen  by  daylight  with 
the  naked  eye  through  the  shafts  of  mines,  and  on  very  high 
mountains,  has  been  with  me  a  subject  of  inquiry  since  my 
early  youth.  I  was  aware  that  Aristotle  had  maintained! 

*  Humboldt,  Relation  Hist,  du  Voyage  aux  Regions  Equinox.,  torn. 
i.,  p.  92-97;  and  Bouguer,  Traiti  d'Optique,  p.  360  and  365.  (Com- 
pare, also,  Captain  Beechey,  in  the  Manual  of  Scientific  Inquiry  for  the 
Use  of  the  Royal  Navy,  1849,  p.  71.) 

t  The  passage  in  Aristotle  referred  to  by  Buffon  occurs  in  a  work 
•where  we  should  have  least  expected  to  find  it — De  Generat.  Animal., 
\.  i.,  p.  780,  Bekker.  Literally  translated,  it  runs  as  follows :  "  Keen- 
ness of  sight  is  as  much  the  power  of  seeing  far  as  of  accurately  distin- 
guishing the  differences  presented  by  the  objects  viewed.  These  two 
properties  are  not  met  with  in  the  same  individuals.  For  he  who  holds 
his  hand  over  his  eyes,  or  looks  through  a  tube,  is  not,  on  that  account, 
more  or  less  able  to  distinguish  differences  of  color,  although  he  will  see 
objects  at  a  greater  distance.  Hence  it  arises  that  persons  in  cavern* 
or  cisterns  are  occasionally  enabled,  to  see  stars."  The  Grecian  'Ooiiy/za- 
ra,  and  more  especially  (ppeara,  are,  as  an  eye-witness,  Professor  Franz, 
observes,  subterranean  cisterns  or  reservoirs  which  communicate  with 
the  light  and  air  by  means  of  a  vertical  shaft,  and  widen  toward  the  bot- 
tom, like  the  neck  of  a  bottle.  Pliny  (lib.  ii.,  cap.  14)  §ays,  "  Altituda 


FISIBILITT    OP    STARS.  57 

that  stars  might  occasionally  be  seen  from  ctverns  and  cis- 
terns, as  through  tubes.  Pliny  alludes  to  the  same  circum- 
stance, and  mentions  the  stars  that  have  been  most  distinctly 
recognized  during  solar  eclipses.  While  practically  engaged 
in  mining  operations,  I  was  in  the  habit,  during  many  years, 
of  passing  a  great  portion  of  the  day  in  mines  where  I  could 
see  the  sky  through  deep  shafts,  yet  I  never  was  able  to  ob- 
serve a  star ;  nor  did  I  ever  meet  with  any  individual  in 
the  Mexican,  Peruvian,  or  Siberian  mines  who  had  heard  of 
stars  having  been  seen  by  daylight ;  although  in  the  many 
latitudes,  in  both  hemispheres,  in  which  I  have  visited  deep 
mines,  a  sufficiently  large  number  of  stars  must  have  passed 
the  zenith  to  have  afforded  a  favorable  opportunity  for  their 
being  seen.  Considering  this  negative  evidence,  I  am  the 
more  struck  by  the  highly  credible  testimony  of  a  celebrated 
optician,  who  in  his  youth  saw  stars  by  daylight  through  the 
shaft  of  a  chimney.*  Phenomena,  whose  manifestation  de- 
pends on  the  accidental  concurrence  of  favoring  circum- 
stances, ought  not  to  be  disbelieved  on  account  of  their 
rarity 

The  same  principle  must,  I  think,  be  applied  to  the  asser- 
tion of  the  profound  investigator  Saussure,  that  stars  have 
been  seen  with  the  naked  eye  in  bright  daylight,  on  the  de- 
clivity of  Mont  Blanc,  and  at  an  elevation  of  12,757  feet 
"  Ctuelques-uns  des  guides  m'ont  assure  avoir  vu  des  etoiles 
en  plein  jour  ;  pour  moi  je  n'y  songeais  pas,  en  sorte  que  je 
n'ai  point  ete  le  temoin  de  ce  phenomene ;  mais  I' assertion 
uniforme  des  guides  ne  me  laisse  aucun  doute  sur  la  rea- 
lite.  II  faut  d'ailleurs  etre  entitlement  a  1'ombre  d'une  epais- 
seur  considerable,  sans  quoi  1'air  trop  fortement  eclaire  fait 
evanouir  la  faible  clarte  des  etoiles."  "  Several  of  the  guides 
assured  me,"  says  this  distinguished  Alpine  inquirer,  "that 

cogit  minores  videri  Stellas ;  affixas  ccelo-solis  fulgor  interdiu  non  cerni, 
quum  aeque  ac  noctu  luceant ;  idque  manifesto m  fiat  defectu  soils  et  prce- 
altis  puteis."  Cleomedes  (  Cycl.  Theor.,  p.  83,  Bake)  does  not  speak  of 
stars  seen  by  day,  but  asserts  "  that  the  sun,  when  observed  from  deep 
cisterns,  appears  larger,  on  account  of  the  darkness  and  the  damp  air." 
*  "  We  have  ourselves  heard  it  stated  by  a  celebrated  optician  that 
the  earliest  circumstance  which  drew  his  attention  to  astronomy  waa 
the  regular  appearance,  at  a  certain  hour,  for  several  successive  days, 
of  a  considerable  star,  through  the  shaft  of  a  chimney." — John  Herschel, 
tlines  of  Astr.,  §  61.  The  chimney-sweepers  whom  I  have  ques- 


Ontlines  of  Astr.,  $  61.  The  chimney-sweepers  whom  I  have  ques- 
tioned agree  tolerably  well  in  the  statement  that "  they  have  never  seen 
stars  by  day,  but  that,  when  observed  at  night,  through  deep  shafts,  the 
sky  appeared  quite  near,  and  the  stars  larger."  I  will  not  enter  upon 
any  discussion  regarding  the  connection  between  these  two  illusions. 


C  2 


58  COSMOS 

they  had  seen  stars  at  broad  daylight :  not  having  myself 
been  a  witness  of  this  phenomenon,  I  did  not  pay  much  at- 
tention to  it,  but  the  unanimous  assertions  of  the  guides  left 
me  no  doubt  of  its  reality.*  It  is  essential,  however,  that 
the  observer  should  be  placed  entirely  in  the  shade,  and  that 
he  should  even  have  a  thick  and  massive  shade  above  his 
head,  since  the  stronger  light  of  the  air  would  otherwise  dis- 
perse the  faint  image  of  the  stars."  These  conditions  are 
therefore  nearly  the  same  as  those  presented  by  the  cisterns 
of  the  ancients,  and  the  chimneys  above  referred  to.  I  do 
not  find  this  remarkable  statement  (made  on  the  moniing  of 
the  2d  of  August,  1787)  in  any  other  description  of  the  Swiss 
mountains.  Two  well-informed,  admirable  observers,  the 
brothers  Hermann  and  Adolph  Schlagentweit,  who  have  re- 
cently explored  the  eastern  Alps  as  far  as  the  summit  of  the 
Gross  Glockner  (13,016  feet),  were  never  able  to  see  stars 
by  daylight,  nor  could  they  hear  any  report  of  such  a  phe- 
nomenon having  been  observed  among  the  goatherds  and 
chamois-hunters.  Although  I  passed  many  years  in  the 
Cordilleras  of  Mexico,  Quito,  and  Peru,  and  frequently  in 
clear  weather  ascended,  in  company  with  Bonpland,  to  ele- 
vations of  more  than  fifteen  or  sixteen  thousand  feet  above 
the  level  of  the  sea,  I  never  could  distinguish  stars  by  day- 
light, nor  was  my  friend  Boussingault  more  successful  in  his 
subsequent  expeditions  ;  yet  the  heavens  were  of  an  azure  so 
intensely  deep,  that  a  cyanometer  (made  by  Paul  of  Geneva) 
which  had  stood  at  39°  when  observed  by  Saussure  on  Mont 
Blanc,  indicated  46°  in  the  zenith  under  the  tropics  at  ele- 
vations varying  between  17,000  and  19,000  feet.f  Under 
the  serene  etherially-pure  sky  of  Cumana,  in  the  plains  near 
the  sea-shore,  I  have  frequently  been  able,  after  observing  an 
eclipse  of  Jupiter's  satellites,  to  find  the  planet  again  with 
the  naked  eye,  and  have  most  distinctly  seen  it  when  the 
gun's  disk  was  from  18°  to  20°  above  the  horizon. 

The  present  would  seem  a  fitting  place  to  notice,  although 
cursorily,  another  optical  phenomenon,  which  I  only  observed 
once  during  my  numerous  mountain  ascents.  Before  sunrise, 
on  the  22d  of  June,  1799,  when  at  Malpays,  on  the  decliv- 
ity of  the  Peak  of  Teneriffe,  at  an  elevation  of  about  11,400 
feet  above  the  sea's  level,  I  observed  with  the  naked  eye 

*  Consult  Saussure,  Voyage  dans  les  Alpes  (Neuchatel,  1779,  4to), 
torn,  iv.,  §  2007,  p.  199. 

t  Humboldt,  Essai  sur  la  G6ographie  des  Plantes,  p.  103.  Compare 
also  my  Voy.  aux  Regions  Equinox,  torn,  i.,  p.  143,  248. 


UNDULATION    OP    THE    STARS.  5» 

cars  near  the  horizon  flickering  with  a  singular  oscillating 
motion.  Luminous  points  ascended,  moved  laterally,  and 
feii  back  to  their  former  position.  This  phenomenon  lasted 
only  from  seven  to  eight  minutes,  and  ceased  long  before  the 
sun's  disk  appeared  above  the  horizon  of  the  sea.  The  same 
.motion  was  discernible  through  a  telescope,  and  there  was 
no  doubt  that  it  was  the  stars  themselves  which  moved.* 
Did  this  change  of  position  depend  on  the  much-contested 
phenomenon  of  lateral  radiation  ?  Does  the  undulation  of 
the  rising  sun's  disk,  however  inconsiderable  it  may  appear 
when  measured,  present  any  analogy  to  this  phenomenon  in 
the  lateral  alteration  of  the  sun's  margin  ?  Independently 
of  such  a  consideration,  this  motion  seems  greater  near  the 
horizon.  This  phenomenon  of  the  undulation  of  the  stars 
was  observed  almost  half  a  century  later  at  the  same  spot 
by  a  well-informed  and  observing  traveler,  Prince  Adalbert 
of  Prussia,  who  saw  it  both  with  the  naked  eye  and  through 
a  telescope.  I  found  the  observation  recorded  in  the  prince's 
manuscript  journal,  where  he  had  noted  it  down,  before  he 
learned,  on  his  return  from  the  Amazon,  that  I  had  wit- 
nessed a  precisely  similar  phenomenon.!  I  was  never  able 
to  detect  any  trace  of  lateral  refraction  on  the  declivities 
of  the  Andes,  or  during  the  frequent  mirages  in  the  torrid 
plains  or  Llanos  of  South  America,  notwithstanding  the  het- 
erogeneous mixture  of  unequally-heated  atmospheric  strata. 
As  the  Peak  of  Tenerifie  is  so  near  us,  and  is  so  frequently 

*  Humboldt,  in  Fr.  von  Zach's  Monatliche  Correspondenz  zur  Erd- 
und  Himmels-Kunde,  bd.  i.,  1800,  s.  396 ;  also  Voy.  aux  R6g.  Equin., 
torn,  i.,  p.  125 :  "  On  croyait  voir  de  petites  fusses  lancees  dans  1'air. 
Des  points  lumineux  eleves  de  7  a  8  degres,  paraissent  d'abord  se  mou- 
voir  dans  le  sens  vertical,  mais  puis  se  convertir  en  une  veritable  oscil- 
lation horizontale.  Ces  images  lumineux  etaient  des  images  de  plu- 
sieurs  etoiles  agrandies  (en  apparence)  par  des  vapeurs  et  revenant  au 
meme  point  d'ou  elles  etaient  partis."  "  It  seemed  as  if  a  number  of 
sinall  rockets  were  being  projected  in  the  air ;  luminous  points,  at  an 
elevation  of  7°  or  8°,  appeared  moving,  first  in  a  vertical,  and  then  os- 
cillating iu  a  horizontal  direction.  These  were  the  images  of  many 
stars,  apparently  magnified  by  vapors,  and  returning  to  the  same  point 
from  which  they  had  emanated." 

t  Prince  Adalbert  of  Prussia,  Aus  meinem  Tagebuche,  1847,  s.  213. 
Is  the  phenomenon  I  have  described  connected  •with  the  oscillations 
of  10"-12",  observed  by  Carlini,  in  the  passage  of  the  polar  star  over 
the  field  of  the  great  Milan  meridian  telescope  ?  (See  Zach's  Corres- 

endance  Astronomique  et  Giog.,  vol.  ii.,  1819,  p.  81.)     Brandes  (Geh- 
's  Umgearb.  Phys.  Wortersb.,  bd.  iv.,  s.  549)  refers  the  phenomenon 
to  mirage.     The  star-like  heliotrope  light  has  also  frequently  been  seen, 
by  the  admirable  and  skillful  observer,  Colonel  Baeyer,  to  oscillate  to 
and  fro  in  a  horizontal  direction. 


60  COSMOS. 

ascended  before  sunrise  by  scientific  travelers  provided  with 
instruments,  I  would  hope  that  this  reiterated  invitation  on 
my  part  to  the  observation  of  the  undulation  of  the  stars 
may  not  be  wholly  disregarded. 

I  have  already  called  attention  to  the  fact  that  the  basis 
of  a  very  important  part  of  the  astronomy  of  our  planetary 
system  was  already  laid  before  the  memorable  years  1608 
and  1610,  and  therefore  before  the  great  epoch  of  the  in- 
vention of  telescopic  vision,  and  its  application  to  astronom- 
ical purposes.  The  treasure  transmitted  by  the  learning  of 
the  Greeks  and  Arabs  was  augmented  by  the  careful  and 
persevering  labors  of  George  Purbach,  Regiomontanus  (i.  e.} 
Johann  Miiller),  and  Bernhard  Walther  of  Niirnberg.  To 
their  efforts  succeeded  a  bold  and  glorious  development  of 
thought — the  Copernican  system  ;  this,  again,  was  followed 
by  the  rich  treasures  derived  from  the  exact  observations  of 
Tycho  Brahe,  and  the  combined  acumen  and  persevering 
spirit  of  calculation  of  Kepler.  Two  great  men,  Kepler  and 
Galileo,  occupy  the  most  important  turning-point  in  the  his- 
tory of  measuring  astronomy ;  both  indicating  the  epoch  that 
separates  observation  by  the  naked  eye,  though  aided  by 
greatly  improved  instruments  of  measurement,  from  tele- 
scopic vision.  Galileo  was  at  that  period  forty-four,  and 
Kepler  thirty-seven  years  of  age  ;  Tycho  Brahe,  the  most 
exact  of  the  measuring  astronomers  of  that  great  age,  had 
been  dead  seven  years.  I  have  already  mentioned,  in  a  pre- 
ceding volume  of  this  work  (see  vol.  ii.,  p.  328),  that  none  of 
Kepler's  cotemporaries,  Galileo  not  excepted,  bestowed  any 
adequate  praise  on  the  discovery  of  the  three  laws  which 
have  immortalized  his  name.  Discovered  by  purely  empir- 
ical methods,  although  more  rich  in  results  to  the  whole  do- 
main of  science  than  the  isolated  discovery  of  unseen  cos- 
mical  bodies,  these  laws  belong  entirely  to  the  period  of  nat- 
ural vision,  to  the  epoch  of  Tycho  Brahe  and  his  observa- 
tions, although  the  printing  of  the  work  entitled  Astronomia 
nova  seu  Physica  codestis  de  motibus  Stella  Martis  was 
not  completed  until  1609,  and  the  third  law,  that  the  squares 
of  the  periodic  times  of  revolution  of  two  planets  are  as  the 
cubes  of  their  mean  distances,  was  first  fully  developed  in 
1619,  in  the  Harmonice  Mundi. 

The  transition  from  natural  to  telescopic  vision  which 
characterizes  the  first  ten  years  of  the  seventeenth  century 
was  more  important  to  astronomy  (the  knowledge  of  the  re- 
gions of  space)  than  the  year  1492  (that  of  the  discoveries 


ASTRONOMICAL    DISCOX  ERIB3.  t51 

of  Columbus)  in  respect  to  our  knowledge  of  terrestrial  space. 
It  not  only  infinitely  extended  our  insight  into  creation,  but 
also,  besides  enriching  the  sphere  of  human  ideas,  raised 
mathematical  science  to  a  previously  unattained  splendor, 
by  the  exposition  of  new  and  complicated  problems.  Thus 
the  increased  power  of  the  organs  of  perception  reacts  on 
the  world  of  thought,  to  the  strengthening  of  intellectual 
force,  and  the  ennoblement  of  humanity.  To  the  telescope 
alone  we  owe  the  discovery,  in  less  than  two  and  a  half 
centuries,  of  thirteen  new  planets,  of  four  satellite-systems 
(the  four  moons  of  Jupiter,  eight  satellites  of  Saturn,  four, 
or  perhaps  six  of  Uranus,  and  one  of  Neptune),  of  the  sun's 
spots  and  faculse,  the  phases  of  Venus,  the  form  and  height 
of  the  lunar  mountains,  the  wintery  polar  zones  of  Mars,  the 
belts  of  Jupiter  and  Saturn,  the  rings  of  the  latter,  the  inte- 
rior planetary  comets  of  short  periods  of  revolution,  together 
with  many  other  phenomena  which  likewise  escape  the  na- 
ked eye.  While  our  own  solar  system,  which  so  long  seemed 
limited  to  six  planets  and  one  moon,  has  been  enriched  in 
the  space  of  240  years  with  the  discoveries  to  which  we 
have  alluded,  our  knowledge  regarding  successive  strata  of 
the  region  of  the  fixed  stars  has  unexpectedly  been  still  more 
increased.  Thousands  of  nebulae,  stellar  swarms,  and  double 
stars,  have  been  observed.  The  changing  position  of  the 
double  stars  which  revolve  round  one  common  center  of 
gravity  has  proved,  like  the  proper  motion  of  all  fixed  starb, 
that  forces  of  gravitation  are  operating  in  those  distant  re- 
gions of  space,  as  in  our  own  limited  mutually-disturbing 
planetary  spheres.  Since  Morin  and  Gascoigne  (not  indeed 
till  twenty-five  or  thirty  years  after  the  invention  of  the  tel- 
escope) combined  optical  arrangements  with  measuring  in- 
struments, we  have  been  enabled  to  obtain  more  accurate 
observations  of  the  change  of  position  of  the  stars.  By  this 
means  we  are  enabled  to  calculate,  with  the  greatest  pre- 
cision, every  change  in  the  position  of  the  planetary  bodies, 
the  ellipses  of  aberration  of  the  fixed  stars  and  their  paral- 
laxes, and  to  measure  the  relative  distances  of  the  double 
stars  even  when  amounting  to  only  a  few  tenths  of  a  sec- 
onds-arc. The  astronomical  knowledge  of  the  solar  system 
has  gradually  extended  to  that  of  a  system  of  the  universe. 
We  know  that  Galileo  made  his  discoveries  of  Jupiter's 
satellites  with  an  instrument  that  magnified  only  seven  diam- 
eters, and  that  he  never  could  have  used  one  of  a  higher 
power  than  thirty-two.  One  hundred  and  seventy  years  later, 


62  COSMOS. 

we  find  Sir  William  Herschel,  in  his  investigations  on  the 
magnitude  of  the  apparent  diameters  of  Arcturus  (0//-2  within 
the  nebula)  and  of  Vega  Lyrte,  using  a  power  of  6500.  Since 
the  middle  of  the  seventeenth  century,  constant  attempts 
have  been  made  to  increase  the  focal  length  of  the  telescope. 
Christian  Huygena,  indeed,  in  1655,  discovered  the  first  sat- 
ellite of  Saturn,  Titan  (the  sixth  in  distance  from  the  center 
of  the  planet),  with  a  twelve-feet  telescope  ;  he  subsequent- 
ly, however,  examined  the  heavens  with  instruments  of  a 
greater  focal  length,  even  of  122  feet ;  but  the  three  object- 
glasses  in  the  possession  of  the  Royal  Society  of  Londonj 
whose  focal  lengths  are  respectively  123,  170,  and  210  feet, 
and  which  were  constructed  by  Constantin  Huygens,  brother 
of  the  great  astronomer,  were  only  tested  by  the  latter,  as 
he  expressly  states,*  upon  terrestrial  objects.  Auzout,  who 
in  1663  constructed  colossal  telescopes  without  tubes,  and 
therefore  without  a  solid  connection  between  the  object-glass 
and  the  eye-piece,  completed  an  object-glass,  which,  with  a 
focal  length  of  320  feet,  magnified  600  times.f  The  most 
useful  application  of  these  object-glasses,  mounted  on  poles, 
was  that  which  led  Dominic  Cassini,  between  the  years  1671 
and  1684,  to  the  successive  discoveries  of  the  eighth,  fifth, 
fourth,  and  third  satellites  of  Saturn.  He  made  use  of  ob- 
ject-glasses that  had  been  ground  by  Borelli,  Campani,  and 
Hartsoeker.  Those  of  the  latter  had  a  focal  length  of  266 
feet. 

During  the  many  years  I  passed  at  the  Paris  Observatory, 
I  frequently  had  in  my  hands  the  instruments  made  by  Cam- 
pani, which  were  in  such  great  repute  during  the  reign  of 
Louis  XIV. ;  and  when  we  consider  the  faint  light  of  Saturn's 
satellites,  and  the  difficulty  of  managing  instruments,  worked 
by  strings  only,|  we  can  not  sufficiently  admire  the  skill  and 
the  untiring  perseverance  of  the  observer. 

*  The  remarkable  artistical  skill  of  Constantin  Huygens,  who  was 
private  secretary  to  King  William  the  Third,  has  only  recently  been 
presented  in  its  proper  light  by  Uytenbrock  in  the  "  Oratio  de  fratribiis 
Christiano  atque  Constantino  Hugenio,  artis  dioptricae  cultoribus,"  1838; 
and  by  Prof.  Kaiser,  the  learned  director  of  the  Observatory  at  Leyden 
(in  Schumacher's  Astron.  Nachr.,  No.  592,  s.  246). 

t  See  Arago,  in  the  Annuaire  pour  1844,  p.  381. 

t  "  Nous  avons  place  ces  grands  verres,  tantot  sur  un  grand  m&t,  tan- 
tot  sur  la  tour  de  bois  venue  de  Marly ;  enfiu  nous  les  avons  mis  dans 
un  tuyau  monte  sur  un  support  en  forme  d'6chelle  &  trois  faces,  ce  qui 
a  eu  (dans  la  decouverte  des  satellites  de  Saturne)  le  succSs  que  nous 
en  avions  esp6r&."  "  We  sometimes  mounted  these  great  instruments 
on  a  high  pole,"  says  Dominique  Caasini,  "  and  sometimes  on  the  wood- 


TELESCOPES.  63 

The  advantages  which  were  at  that  period  supposed  to 
be  obtainable  only  by  gigantic  length,  led  great  minds,  as  is 
frequently  the  case,  to  extravagant  expectations.  Auzout 
considered  it  necessary  to  refute  Hooke,  who  is  said  to  have 
proposed  the  use  of  telescopes  having  a  length  of  upward  of 
10,000  feet  (or  nearly  two  miles),*  in  order  to  see  animals 
in  the  moon.  A  sense  of  the  practical  inconvenience  of  op- 
tical instruments  having  a  focal  length  of  more  than  a  hund- 
red feet,  led,  through  the  influence  of  Newton  (in  following 
out  the  earlier  attempts  of  Mersenne  and  James  Gregory  of 
Aberdeen),  to  the  adoption,  especially  in  England,  of  shorter 
reflecting  telescopes.  The  careful  comparison  made  by  Brad- 
ley and  Pond,  of  Hadley's  five-feet  reflecting  telescopes,  with 
the  refractor  constructed  by  Constantin  Huygens  (which 
had,  as  already  observed,  a  focal  length  of  123  feet),  fully 
demonstrated  the  superiority  of  the  former.  Short's  expens- 
ive reflectors  were  now  generally  employed  until  1759,  when. 
John  Dollond's  successful  practical  solution  of  the  problem 
of  achromatism,  to  which  he  had  been  incited  by  Leonhard 
Euler  and  Klingenstierna,  again  gave  preponderance  to  re- 
fracting instruments.  The  right  of  priority,  which  appears 
to  have  incontestably  belonged  to  the  mysterious  Chester 
More,  Esq.,  of  More  Hall,  in  Essex  (1729),  was  first  made 
known  to  the  public  when  John  Dollond  obtained  a  patent 
for  his  achromatic  telescopes. f 

The  triumph  obtained  by  refracting  instruments  was  not, 
however,  of  long  duration.  In  eighteen  or  twenty  years  after 
the  construction  of  achromatic  instruments  by  John  Dollond, 
by  the  combination  of  crown  with  flint  glass,  new  fluctua- 

en  tower  that  had  been  brought  from  Marly ;  and  we  also  placed  them 
in  a  tube  mounted  on  a  three-sided  ladder,  a  method  which,  in  the  dis- 
covery of  the  satellites  of  Saturn,  gave  us  all  the  success  we  had  hoped." 
— Delambre,  Hist,  de  VAstr.  Moderne,  torn,  ii.,  p.  785.  Optical  instru- 
ments having  such  enormous  focal  lengths  remind  us  of  the  Arabian  in- 
struments olmeasurement— -quadrants  with  a  radius  of  about  190  feet, 
upon  whose  graduated  limb  the  image  of  the  sun  was  received  as  in  the 
gnomon,  through  a  small  round  aperture.  Such  a  quadrant  was  erect- 
ed at  Samarcand,  probably  constructed  after  the  model  of  the  older  sex- 
tants of  Al-Chokandi  (which  were  about  60  feet  in  height).  Compare 
Sedillot,  P 'rottgomenes  det  Tables  d'Oloug-Beg,  1847,  p.  Ivii.  and  cxxix. 

*  See  Delambre,  Hist,  de  VAstr.  Mod.,  t.  ii.,  p.  594.  The  mystic 
Capuchin  monk,  Schyrle  von  Rheita,  who,  however,  was  well  versed 
in  optics,  had  already  spoken  in  his  work,  Oculus  Enoch  et  Elite  (Autv., 
1645),  of  the  speedy  practicability  of  constructing  telescopes  that  should 
magnify  4000  times,  by  means  of  which  the  lunar  mountains  might  b« 
accurately  laid  down.  Compare  also  Cosmos,  vol.  ii.,  p.  323  (note). 

t  Edinb.  Encyclopedia,  vol.  xx.,  p.  479. 


tions  of  opinion  were  excited  by  the  just  admiration  award- 
ed, both  at  home  and  abroad,  to  the  immortal  labors  of  a 
German,  William  Herschel.  The  construction  of  numerous 
seven-feet  and  twenty-feet  telescopes,  to  which  powers  of 
from  2200  to  6000  could  be  applied,  was  followed  by  that  of 
his  forty-feet  reflector.  By  this  instrument  he  discovered,  in 
August  and  September,  1789,  the  two  innermost  satellites 
of  Saturn — Enceladus,  the  second  in  order,  and^soon  after- 
ward, Mimas,  the  first,  or  the  one  nearest  to  the  ring.  The 
discovery  of  the  planet  Uranus  in  1781  was  made  with 
Herschel's  seven-feet  telescope,  while  the  faint  satellites  of 
this  planet  were  first  observed  by  him  in  1787,  with  a  twen- 
ty-feet "front  view"  reflector.*  The  perfection,  unattained 
till  then,  which  this  great  man  gave  to  his  reflecting  tele- 
scopes, in  which  light  was  only  once  reflected,  led,  by  the 
uninterrupted  labor  of  more  than  forty  years,  to  the  most 
important  extension  of  all  departments  of  physical  astron- 
omy in  the  planetary  spheres,  no  less  than  in  the  world  of 
nebulae  and  double  stars. 

The  long  predominance  of  reflectors  wus  followed,  in  the 
earlier  part  of  the  nineteenth  century,  by  a  successful  emu- 
lation in  the  construction  of  achromatic  refractors,  and  heli- 
ometers,  paralactically  moved  by  clock-work.  A  homoge- 
neous, perfectly  smooth  flint  glass,  for  the  construction  of 
object-glasses  of  extraordinary  magnitude,  was  manufactured 
in  the  institutions  of  Utzschneider  and  Fraunhofer  at  Mu- 
nich, and  subsequently  in  those  of  Merz  and  Mahler  ;  and  in 
the  establishments  of  Guinand  and  Bontems  (conducted  for 
MM.  Lerebours  and  Cauchoix)  in  Switzerland  and  France. 
It  will  be  sufficient  in  this  historical  sketch  to  mention,  by 
way  of  example,  the  large  refractors  made  under  Fraunho- 
fer's  directions  for  the  Observatories  of  Dorpat  and  Berlin, 
in  which  the  clear  aperture  was  9' 6  inches  in  diameter,  with 
a  focal  length  of  14 '2  feet,  and  those  executed  by  Merz  and 
Mahler  for  the  Observatories  of  Pulkowa  and  Cambridge,  in 
the  United  States  of  America  ;t  they  are  both  adjusted  with 

*  Consult  htruve,  Etudes  d'Astr.  Stellaire,  1847,  note  59,  p.  24.  I 
have  retained  the  designations  of  forty,  twenty,  and  seven-feet  Herschel 
reflecting  telescopes,  although  in  other  parts  of  the  work  (the  original 
German)  I  have  used  French  measurements.  I  have  adopted  these 
designations  not  merely  on  account  of  their  greater  convenience,  but 
also  because  they  have  acquired  historical  celebrity  from  the  important 
labors  both  of  the  elder  and  younger  Herschel  in  England,  and  of  the 
latter  at  Feldhausen,  at  the  Cape  of  Good  Hope. 

t  See  Schumacher's  Astr.  Nachr.,  No.  371  and  611.     Cauchoix  and 


TELESCOPES.  65 

object-glasses  of  15  inches  in  diameter,  and  a  focal  length 
of  22-5  feet.  The  heliometer  at  the  Konigsberg  Observa- 
tory, which  continued  for  a  long  time  to  be  the  largest  in 
existence,  has  an  aperture  of  6'4  inches  in  diameter.  This 
instrument  has  been  rendered  celebrated  by  the  memorable 
labors  of  Bessel.  The  well-illuminated  and  short  dyalitic 
refractors,  which  were  first  executed  by  Plosl  in  Vienna: 
and  the  advantages  of  which  were  almost  simultaneously 
recognized  by  Rogers  in  England,  are  of  sufficient  merit  to 
warrant  their  construction  on  a  large  scale. 

During  this  period,  to  the  efforts  of  which  I  have  refer- 
red, because  they  exercised  so  essential  an  influence  on  the 
extension  of  cosmical  views,  the  improvements  made  in  in- 
struments of  measurement  (zenith  sectors,  meridian  circles, 
and  micrometers)  were  as  marked  in  respect  to  mechanics  as 
they  were  to  optics  and  to  the  measurement  of  time.  Among 
the  many  names  distinguished  in  modern  times  in  relation 
to  instruments  of  measurement,  we  will  here  only  mention 
those  of  Ramsden,  Troughton,  Fortin,  Reichenbach,  Gam- 
bey,  Ertel,  Steinheil,  Repsold,  Pistor,  and  Oertling  ;  in  rela- 
tion to  clironometers  and  astronomical  pendulum  clocks,  we 
may  instance  Mudge,  Arnold,  Emery,  Earnshaw,  Breguet, 
.Rirgens^n,  Kessels,  "Winnerl,  and  Tiede  ;  while  the  noble  la- 
Ws  of  \Yilliam  and  John  Herschel,  South,  Struve,  Bessel, 
and  Dawes,  in  relation  to  the  distances  and  periodic  motions 
of  the  double  stars,  specially  manifest  the  simultaneous  per- 
fection acquired  in  exact  vision  and  measurement.  Struve's 
classification  of  the  double  stars  gives  about  100  for  the  num- 
ber whose  distance  from  one  another  is  below  1",  and  336 
for  those  between  1"  and  2"  ;  the  measurement  in  every  case 
being  several  times  repeated.* 

During  the  last  few  years,  two  men,  unconnected  with 
any  industrial  profession — the  Earl  of  Rosse,  at  Parson's 
Town  (about  fifty  miles  west  of  Dublin),  and  Mr.  Lassell,  at 
Starfield,  near  Liverpool,  have,  with  the  most  unbounded 
liberality,  inspired  with  a  noble  enthusiasm  for  the  cause  of 
science,  constructed  under  their  own  immediate  superintend- 
ence two  reflectors,  which  have  raised  the  hopes  of  astron- 
omers to  the  highest  degree. t  Lassell's  telescope,  which  has 

Lerebours  have  also  constructed  object-glasses  of  more  than  13 -3  inches 
in  diameter,  and  nearly  25  feet  focal  length. 

*  Struve,  Stellarum  duplicium  el  multiplicium  Mensurce  Micrometricee, 
p.  2,  41. 

t  Mr.  Airy  has  recently  given  a  comparative  description  of  the  meth- 
ods of  constructing  these  two  telescopes,  including  an  account  of  the 


66  COSMOS. 

an  aperture  only  two  feet  in  diameter,  with  a  focal  length 
of  twenty  feet,  has  already  been  the  means  of  discovering 
one  satellite  of  Neptune,  and  an  eighth  of  Saturn,  besides 
which  two  satellites  of  Uranus  have  been  again  distinguish- 
ed. The  new  colossal  telescope  of  Lord  Rosse  has  an  aper- 
ture of  six  feet,  and  is  fifty-three  feet  in  length.  It  is  mount- 
ed in  the  meridian  between  two  walls,  distant  twelve  feet 
011  either  side  from  the  tube,  and  from  forty-eight  to  fifty-six 
feet  in  height.  Many  nebulae,  which  had  been  irresolvable 
by  any  previous  instruments,  have  been  resolved  into  stellar 
swarms  by  this  noble  telescope  ;  while  the  forms  of  other 
nebulae  have  now,  for  the  first  time,  been  recognized  in  their 
true  outlines.  A  marvelous  effulgence  is  poured  forth  from 
the  speculum. 

The  idea  of  observing  the  stars  by  daylight  with  a  tele- 
scope first  occurred  to  Morin,  who,  with  Gascoigne  (about 
1638,  before  Picard  and  Auzout),  combined  instruments  of 
measurement  with  the  telescope.  Morin  himself  says,*  "It 
was  not  Tycho's  great  observations  in  reference  to  the  posi- 
tion of  the  fixed  stars,  when,  in  1582,  twenty-eight  years 
before  the  invention  of  the  telescope,  he  was  led  to  compare 
Venus  by  day  with  the  sun,  and  by  night  with  the  stars," 
but  "  the  simple  idea  that  Arcturus  and  other  fixed  stars 
might,  like  Venus,  when  once  they  had  been  fixed  in  the 
field  of  the  telescope  before  sunrise,  be  followed  through  the 
heavens  after  the  sun  had  risen,  that  led  him  to  a  discovery 
which  might  prove  of  importance  for  the  determination  of 
longitude  at  sea."  No  one  was  able  before  him  to  distin- 
guish the  fixed  stars  in  the  presence  of  the  sun.  Since  the 

mixing  of  the  metal,  the  contrivances  adopted  for  casting  and  polishing 
the  specula  and  mounting  the  instruments. — Abatr.  of  the  Astr.  Soc., 
vol.  ix.,  No.  5,  March,  1849.  The  effect  of  Lord  Rosse's  six  feet  metal- 
lic reflector  is  thus  referred  to  (p.  120):  "The  astronomer  royal,  Mr. 
Airy,  alluded  to  the  impression  made  by  the  enormous  light  of  the  tel- 
escope ;  partly  by  the  modifications  produced  in  the  appearances  of 
nebulas  already  figured,  partly  by  the  great  number  of  stars  seen  even 
at  a  distance  from  the  Milky  Way,  and  partly  from  the  prodigious  brill- 
iancy of  Saturn.  The  account  given  by  another  astronomer  of  the  ap- 
pearance of  Jupiter  was,  that  it  resembled  a  coach-lamp  in  the  tele- 
scope; and  this  well  expresses  the  blaze  of  light  which  is  seen  in  the 
instrument."  Compare  also  Sir  John  Herschel,  Oull.  of  Astr.,  §  870. 
"  The  sublimity  of  the  spectacle  afforded  by  the  magnificent  reflecting 
telescope  constructed  by  Lord  Rosse  of  some  of  the  larger  globular  clus- 
ters of  nebulae,  is  declared  by  all  who  have  witnessed  it  to  be  such  as 
no  words  can  express.  This  telescope  has  resolved  or  rendered  resolv- 
able multitudes  of  nebula?  which  had  resisted  all  inferior  powers." 
*  Delambre,  Hist,  de  V  Astr  on.  Moderne,  t.  ii.,  p.  255. 


TELESCOPES.  67 

employment,  by  Homer,  of  great  meridian  telescopes  in  1691, 
observations  of  the  stars  by  day  have  been  frequent  and  fruit- 
ful in  results,  having  been,  in  some  cases,  advantageously 
applied  to  the  measurement  of  the  double  star's.  Struve 
states*  that  he  has  determined  the  smallest  distances  of  ex- 
tremely faint  stars  in  the  Dorpat  refractor,  with  a  power  of 
only  320,  in  so  bright  a  crepuscular  light  that  he  could  read 
with  ease  at  midnight.  The  polar  star  has  a  companion  of 
the  ninth  magnitude,  which  is  situated  at  only  18"  distance  : 
it  was  seen  by  day  in  the  Dorpat  refracting  telescope  by 
Struve  and  Wrangel,f  and  was  in  like  manner  observed  on 
one  occasion  by  Encke  and  Argelander. 

Many  conjectures  have  been  hazarded  regarding  the  cause 
of  the  great  power  of  the  telescope  at  a  time  when  the  dif- 
fused light  of  the  atmosphere,  by  multiplied  reflection,  ex- 
erts an  obstructing  action.^  This  question,  considered  as  an 

*  Strove,  Metis.  Microm.,  p.  xliv. 

t  Schumacher's  Jahrbuchfur  1839,  s.  100. 

j  La  lumiere  atmospherique  diffuse  ne  peut  s'expliquer  par  le  reflet 
des  rayons  solaires  sur  la  surface  de  separation  des  couches  de  difleren- 
tes  densites  dont  on  suppose  1'atmosphere  composee.  En  eflet,  suppo- 
sons  le  soleil  place  a  1'horizon,  les  surfaces  de  separation  dans  la  direc- 
tion du  zenith  seraient  horizontales,  par  consequent  la  reflexion  serait 
horizontale  aussi,  et  nous  ne  verrions  aucune  lumiere  au  zenith.  Dana 
la  supposition  des  couches,  aucun  rayon  ne  nous  arriverait  par  voie 
d'une  premiere  reflexion.  Ce  ne  seraient  que  les  reflexions  multiples 
qui  pourraient  agir.  Done  pour  expliquer  la  lumiere  diffuse,  il  faut  se 
figurer  1'atmosphere  composee  de  molecules  (spheriques,  par  exemple) 
dont  chacune  uonne  une  image  du  soleil  a  peu  pres  comme  les  boulea 
de  verres  que  nous  plasons  dans  nos  jardius.  L'air  pur  est  bleu,  par- 
ceque  d'apres  Newton,  les  molecules  de  1'air  ont  Vepaisseur  qui  convi- 
ent  a  la  reflexion  des  rayons  bleus.  II  est  done  naturel  que  les  petites 
images  du  soleil  que  de  tous  cotes  reflechissent  les  molecules  sphe- 
riques de  1'air  et  qui  sont  la  lumiere  diffuse  aient  une  teinte  bleue : 
mais  ce  bleu  n'est  pas  du  bleu  pur,  c'est  uu  blanc  dans  lequel  le  bleu 
predomine.  Lorsque  le  ciel  n'est  pas  dans  toute  sa  purete  et  que  1'air 
est  me!6  de  vapeurs  visibles,  la  lumiere  diffuse  resoit  beaucoup  de 
blanc.  Comme  la  lune  est  jaune,  le  bleu  de  1'air  pendant  la  nuit  est  un 
peu  verdatre,  c'est-a-dire,  melange  de  bleu  et  de  jaune." 

"  We  can  not  explain  the  diffusion  of  atmospheric  light  by  the  reflec- 
tion of  solar  rays  on  the  surface  of  separation  of  the  strata  of  different 
density,  of  which  we  suppose  the  atmosphere  to  be  composed.  In  fact, 
if  we  suppose  the  sun  to  be  situated  on  the  horizon,  the  surfaces  of  sep- 
aration in  the  direction  of  the  zenith  will  be  horizontal,  and  consequent- 
ly the  reflection  would  likewise  be  horizontal,  and  we  should  not  be 
able  to  see  any  light  at  the  zenith.  On  the  supposition  that  such  strata 
exist,  no  ray  would  reach  us  by  means  of  direct  reflection.  Repeated 
reflections  would  be  necessary  to  produce  any  effect.  In  order,  there- 
fore, to  explain  the  phenomenon  of  diffused  light,  we  must  suppose  the 
atmosphere  to  be  composed  of  molecules  (of  a  spherical  form,  for  in 


68  COSMOS. 

optical  problem,  excited  the  strongest  interest  in  the  mind  of 
Bessel,  whose  too  early  death  was  so  unfortunate  for  the 
cause  of  science.  In  his  long  correspondence  with  myself,  he 
frequently  reverted  to  this  subject,  admitting  that  he  could 
not  arrive  at  any  satisfactory  solution.  1  feel  confident  it 
will  not  be  unwelcome  to  my  readers  if  I  subjoin,  in  the 
form  of  a  note,  some  of  the  opinions  of  Arago,*  as  expressed 

stance),  each  of  which  presents  an  image  of  the  sun  somewhat  in  the 
game  manner  as  an  ordinary  glass  ball.  Pure  air  is  blue,  because,  ac- 
cording to  Newton,  the  molecules  of  the  air  have  the  thickness  neces 
sary  to  reflect  blue  rays.  It  is  therefore  natural  that  the  small  images  of 
the  sun,  reflected  by  the  spherical  molecules  of  the  atmosphere,  should 
present  a  bluish  tinge ;  this  color  is  not,  however,  pure  blue,  but  white, 
in  which  the  blue  predominates  When  the  sky  is  not  perfectly  pure 
and  the  atmosphere  is  blended  with  perceptible  vapors,  the  diffused 
light  is  mixed  with  a  large  proportion  of  white.  As  the  moon  is  yellow, 
the  blue  of  the  air  assumes  somewhat  of  a  greenish  tinge  by  night,  or, 
in  other  words,  becomes  blended  with  yellow." — MSS.  of  1847. 

*  D'vn  des  Effcts  dcs  Lunettes  sur  la  Visibility  des  etoiles.  (Lctlre  de 
M.  Arago  a  M.  de  Humboldt  en  Die.,  1847.) 

"  L'ceil  n'est  done  que  d'une  sensibilite  circonscrite,  bornee.  Quand 
la  lumiere  qui  frappe  la  retine,  n'a  pas  assez  d'intensite,  1'oeil  ne  sent 
rien.  C'est  par  un  manque  d'intensite  que  beaucoup  d.' etoiles,  mdme 
dans  les  nuits  les  plus  profondes  echappent  a  nos  observations.  Les  lu- 
nettes ont  pour  effet,  quant  aux  etoiles,  d'augmenter  1'intensite  de  1'image. 
Le  faisceau  cylindrique  de  rayons  paralleles  venant  d'une  etoile,  qui 
s'appuie  sur  la  surface  de  la  lentille  objective,  et  qui  a  cette  surface  cir- 
culaire  pour  base,  se  trouve  considerablement  resserre  a  la  sortie  de  la 
lentille  oculaire.  Le  diametre  du  premier  cylindre  est  au  diametre 
du  second,  comme  la  distance  focale  de  1'objectif  est  a  la  distance  fo- 
cale  de  Poculaire,  ou  bieu  comme  le  diametre  de  1'objectif  est  au  dia- 
metre de  la  portion  d'oculaire  qu'occupe  le  faisceau  emergent.  Les  iii- 
tensites  de  lumiere  dans  les  deux  cylindres  en  question  (dans  les  deux 
cylindres,  incident  et  emergent)  doiveut  etre  entr'elles  comme  les  eten- 
dues  superficielles  des  bases.  Ainsi  la  lumiere  emergente  sera  plus  con- 
densee,  plug  intense  que  la  lumiere  naturelle  tombant  sur  1'objectif,  dans 
le  rapport  de  la  surface  de  cet  objectif  a  la  surface  circulaire  de  la  base 
du  faisceau  emergent.  Le  faisceau  Emergent,  quand  la  lunette  grosrit, 
etant  plus  etroit  que  le  faisceau  cylindrique  qui  tombe  sur  1'objectif,  il 
est  evident  que  la  pupille,  quelle  que  soit  son  cMverture,  recueillera  plus 
de  rayons  par  1'intermediaire  de  la  lunette  que  sans  elle.  La  lunette 
augmentera  done  toujours  1'intensite  de  la  lumiere  des  ttoilei. 

"  Le  cas  le  plus  favorable,  quant  a  1'effet  des  lunettes,  est  evidemment 
celui  ou  1'ceil  re9oit  la  totalite  du  faisceau  emergent,  le  cas  ou  ce  fais- 
ceau a  moins  de  diametre  que  la  pupille.  Alors  toute  la  lumiire  que 
1'objectif  embrasse,  concourt,  par  1'entremise  du  telescope,  a  la  forma- 
tion de  1'image.  A  1'ceil  nu,  au  contraire,  une  portion  seule  de  cetto 
meme  lumiere  est  mise  a  profit ;  c'est  la  petite  portion  que  la  surface 
de  la  pupille  decoupe  dans  le  faisceau  incident  naturel.  L'intensit^  do 
1'image  telescopique  d'une  etoile  est  done  &  1'intensite  de  1'image  & 
1'ceil  nu,  comme  la  surface  de  1'objectif  est  a  celle  de  la  pupille. 

"  Ce  qui  precede  est  relatif  a  la  visibilite  d'uu  seul  point,  d'uno  seulo 


TELESCOPES.  69 

in  one  of  the  numerous  manuscripts  to  which  I  was  permit- 
ted free  access  during  my  frequent  sojourn  in  Paris.     Ac- 

etoile.  Venons  a  1'observation  d'un  objet  ayant  des  dimensions  an 
gulair«w  seusibles,  a  1'observation  d'une  planete.  Dans  les  cas  les  plus 
lavorables,  c'est-a-dire  lorsque  la  pupille  re^oit  la  totalite  du  pinceaa 
emergeut,  1'intensite  de  1'image  de  ckaque  point  de  la  planete  se  calcu- 
lera  par  la  proportion  que  nous  venons  de  donner.  La  quantite  totalt 
de  lumiere  concourant  a  former  V ensemble  de  1'image  a  Tceil  nu,  sera 
done  aussi  a  la  quantite  totale  de  lumiere  qui  forme  1'image  de  la  pla- 
nete A  1'aide  d'uue  lunette,  comme  la  surface  de  la  pupille  est  4  la  sur- 
face de  1'obiectif.  Les  intensites  comparatives,  non  plus  de  pointe 
isoles,  mais  des  deux  images  d'une  planete,  qui  se  forment  sur  la  retina 
a  1'oeil  nu,  et  par  I'iutermediaire  d'une  lunette,  doivent  evidemment 
diminuer  proportionuellement  aux  etendues  superficielles  de  ces  deux  im- 
ages. Les  dimensions  lineaires  des  deux  images  sont  entr'elles  comme 
le  diametre  de  1'objectif  est  au  diametre  du  faisceau  emergent.  Le 
nouibre  de  fois  que  la  surface  de  1'image  amplifiee  surpasse  la  surface 
de  1'image  a  1'oeil  nu,  s'obtiendra  done  en  divisant  le  carre  du  diametre 
de  1'objeclifpa.r  le  carre  du  diametre  du  faisceau  Emergent,  ou  bien  la  sur- 
face de  I'objeclif par  la  surface  de  la  base  circulaire  du  faisceau  emergent. 
"  Nous  avons  deja  obtenu  le  rapport  des  quantites  totales  de  lumiere 
qui  engendrent  les  deux  images  d'une  planete,  en  divisant  la  surface  de 
1'objectif  par  la  surface  de  la  pupille.  Ce  nombre  est  plus  petit  que  le 
quotient  auquel  on  arrive  en  divisant  la  surface  de  1'objectif  par  la  sur- 
face du  faisceau  Emergent.  II  en  resulte,  quant  aux  planetes,  qu'une 
lunette  lait  moins  gagtier  en  intensite  de  lumiere,  qu'elle  ne  fait  perdre 
en  agrandissaut  la  surface  des  images  sur  la  retine;  1'intensite  de  ces 
images  doit  done  aller  continuellement  en  s'afiaiblissant  a  mesure  que 
le  pouvoir  amplificatif  de  la  lunette  ou  du  telescope  s'accroit. 

"  L'atmosphere  peut  etre  consideree  comme  une  planete  a  dimen- 
sions indefiuies.  La  portion  qu'on  en  verra  dans  une  lunette,  subira 
done  aussi  la  loi  d'affaiblissement  que  nous  venons  d'indiquer.  Le  rap* 
port  entre  1'intensite  de  la  lumiere  d'une  planete  et  le  champ  de  lumiere 
atinospherique  a  travers  lequel  on  la  verra,  sera  le  memo  a  1'ceil  nu  et 
dans  les  lunettes  de  tous  les  grossissements,  de  toutes  les  dimensions. 
Les  lunettes,  sous  le  rapport  de  Vintensite,  ne  favorisent  done  pas  la  visi- 
bilite  des  planetes. 

"  II  n'eu  est  point  ainsi  des  etoiles.  L'intensite  de  1'image  d'une  etoile 
est  plus  forte  avec  une  lunette  qu'a  I'o3il  nu ;  au  contraire,  le  champ  de 
la  vision,  uuiformement  eclaire  dans  les  deux  cas  par  la  lumiere  atmos- 
pherique,  est  plus  clair  a  I'osil  nu  que  dan«  la  lunette.  II  y  a  done  deux 
raisons,  sans  sortir  des  considerations  d'intensite,  pour  que  dans  une  lu- 

ette  de  1'image  de  1'etoile  predomine  sur  celle  de  1'atmosphere,  nota- 

lement  plus  qu'a  I'oail  nu. 


"  Cette  predominance  doit  aller  graduellement  en  augmentant  avec 
le  grossissement.  En  efiet,  abstraction  faite  de  certaine  augmentation 
du  diametre  de  1'etoile,  consequence  de  divers  effets  de  diffraction  ou 
d1 'interferences,  abstraction  faite  aussi  d'une  plus  forte  reflexion  que  la 
lumiere  subit  sur  les  surfaces  plus  obliques  des  oculaires  de  tres  courts 
foyers,  V intensite  dc  la  lumiere  de  Vetoile  est  constante  tant  que  1'ouver- 
ture  de  1'objectif  ne  varie  pas.  Comme  ou  1'a  vu,  la  clarte  du  champ 
de  la  lunette,  au  contraire,  diminue  sans  cesse  a  mesure  que  le  pouvoir 
amplificatif  s'accroit.  Done  toutes  autres  circoustances  restant  egales, 
uue  etoile  sera  d'autant  p.1'!*  visible,  sa  predouiiuence  sur  la  lumiere  tin 


70  COSMOS. 

cording  to  the  ingenious  explanation  of  my  friend,  high  rnag» 
nify ing  powers  facilitate  the  discovery  and  recognition  of  the 

champ  du  telescope  sera  d'autaut  plus  tranchee  qu'on  lera  usage  d'un 
grossissemont  plus  fort." 

"  The  eye  is  endowed  with  only  a  limited  sensibility ;  for  when  the 
light  which  strikes  the  retina  is  not  sufficiently  strong,  the  eye  is  not 
sensible  of  any  impression.  In  consequence  of  deficient  intensity,  many 
stars  escape  our  observation,  even  in  the  darkest  nights.  Telescopic 
glasses  have  the  effect  of  augmenting  the  intensity  of  the  images  of  the 
stars.  The  cylindrical  pencil  of  parallel  rays  emanating  from  a  star, 
and  striking  the  surface  of  the  object-glass,  on  whose  circular  surface  it 
rests  as  on  abase,  is  considerably  contracted  on  emerging  from  the  eye- 
piece. The  diameter  of  the  first  cylinder  is  to  that  of  the  second  as 
the  focal  distance  of  the  object-glass  is  to  the  focal  distance  of  the  eye- 
piece, or  as  the  diameter  of  the  object-glass  is  to  the  diameter  of  tho 
part  of  the  eye-piece  covered  by  the  emerging  rays.  The  intensities 
of  the  light  in  these  two  cylinders  (the  incident  and  emerging  cylin- 
ders) must  be  to  one  another  as  the  superficies  of  their  bases.  Thus, 
the  emerging  light  will  be  more  condensed,  more  intense,  than  the  nat- 
ural light  falling  on  the  object-glass,  in  the  ratio  of  the  surface  of  this 
object-glass  to  the  circular  surface  of  the  base  of  this  emerging  pencil. 
As  the  emerging  pencil  is  narrower  in  a  magnifying  instrument  than  the 
cylindrical  pencil  falling  on  the  object-glass,  it  is  evident  that  the  pupil, 
whatever  may  be  its  aperture,  will  receive  more  rays,  by  the  interven- 
tion of  the  telescope,  than  it  could  without.  The  intensity  of  the  light 
of  the  stars  will,  therefore,  always  be  augmented  when  seen  through  a 
telescope. 

"  The  most  favorable  condition  for  the  use  of  a  telescope  is  undoubt 
edly  that  in  which  the  eye  receives  the  whole  of  the  emerging  rays, 
and,  consequently,  when  the  diameter  of  the  pencil  is  less  than  that  of 
the  pupil.  The  whole  of  the  light  received  by  the  object-glass  then  co- 
operates, through  the  agency  of  the  telescope,  in  the'  formation  of  the 
image.  In  natural  vision,  on  the  contrary,  a  portion  only  of  this  light 
is  rendered  available,  namely,  the  small  portion  which  enters  the  pupil 
naturally  from  the  incident  pencil.  The  intensity  of  the  telescopic  im 
age  of  a  star  is,  therefore,  to  the  intensity  of  the  image  seen  with  the 
naked  eye,  as  the  surface  of  the  object-glass  is  to  that,  of  the  pupil. 

"  The  preceding  observations  relate  to  the  visibility  of  one  point  or 
one  star.  We  will  now  pass  on  to  the  consideration  of  an  o*bject  having 
sensible  angular  dimensions,  as,  for  instance,  a  planet.  Under  the  most 
favorable  conditions  of  vision,  that  is  to  say,  when  the  pupil  receives 
the  whole  of  the  emerging  pencil,  the  intensity  of  each  point  of  the  plan- 
et's image  may  be  calculated  by  the  proportions  we  have  already  given. 
The  total  quantity  of  light  contributing  to  form  the  whole  of  the  image, 
as  seen  by  the  naked  eye,  will,  therefore,  be  to  the  total  quantity  of  the 
light  forming  the  image  of  the  planet  by  the  aid  of  a  telescope,  as  the 
surface  of  the  pupil  is  to  the  surface  of  the  object-glass.  The  compar- 
ative intensities,  not  of  mere  isolated  points,  but  of  the  images  of  a  plan- 
et formed  respectively  on  the  retina  of  the  naked  eye,  and  by  the  in- 
tervention of  a  telescope,  must  evidently  diminish  proportionally  to  the 
superficial  extent  of  these  two  images.  The  linear  dimensions  of  the 
two  images  are  to  one  another  as  the  diameter  of  the  object-glass  is  to 
that  of  the  emerging  pencil.  We  therefore  obtain  the  number  of  times 
that  the  surface  of  the  magnified  image  exceeds  the  surface  of  the  iui- 


TELESCOPES.  71 

fixed  stars,  since  they  convey  a  greater  quantity  of  intense 
light  to  the  eye  without  perceptibly  enlarging  the  image  ; 

age  when  seen  by  the  naked  eye  by  dividing  the  square  of  the  diameter 
of  the  object-glass  by  the  square  of  the  diameter  of  the  emerging  pencil,  or 
rather  the  surface  of  the  abject-glass  by  the  surface  of  the  circular  bate 
of  the  emerging  pencil. 

"  By  dividing  the  surface  of  the  object-glass  by  the  surface  of  the  pu 
pil,  \ve  have  already  obtained  the  ratio  of  the  total  quantities  of  light 
produced  by  the  two  images  of  a  planet.  This  number  is  lower  than 
the  quotient  which  we  obtain  by  dividing  the  surface  of  the  object- 
glass  by  the  surface  of  the  emerging  pencil.  It  follows,  therefore,  with 
respect  to  planets,  that  a  telescope  causes  us  to  gain  less  in  intensity  of 
light  than  is  lost  by  magnifying  the  surface  of  the  images  on  the  retina; 
the  intensity  of  these  images  must  therefore  become  continually  fainter, 
in  proportion  as  the  magnifying  power  of  the  telescope  increases. 

"  The  atmosphere  may  be  considered  as  a  planet  of  indefinite  dimen- 
sions. The  portion  of  it  that  we  see  in  a  telescope  will  therefore  also 
be  subject  to  the  same  law  of  diminution  that  we  have  indicated.  The 
relation  between  the  intensity  of  the  light  of  a  planet  and  the  field  of  at- 
mospheric light  through  which  it  is  seen,  will  be  the  same  to  the  naked 
eye  and  in  telescopes,  whatever  may  be  their  dimensions  and  magnify- 
ing powers.  Telescopes,  therefore,  do  not  favor  the  visibility  of  planets 
in  respect  to  the  intensity  of  their  light. 

"  The  same  is*  not  the  case  with  respect  to  the  stars.  The  intensity 
of  the  image  of  a  star  is  greater  when  seen  with  the  telescope  than  with 
the  naked  eye ;  the  field  of  vision,  on  the  contrary,  uniformly  illumined 
in  both  cases  by  the  atmospheric  light,  is  clearer  in  natural  than  in  tel- 
escopic vision.  There  are  two  reasons,  then,  which,  in  connection  with 
the  consideration  of  the  intensity  of  light,  explain  why  the  image  of  a 
star  preponderates  in  a  telescope  rather  than  in  the  naked  eye  over  that 
of  the  atmosphere. 

"  This  predominance  must  gradually  increase  with  the  increased 
magnifying  power.  In  fact,  deducting  the  constant  augmentation  of 
the  star's  diameter,  consequent  upon  the  different  effects  of  diffraction 
or  interference,  and  deducting  also  the  stronger  reflection  experienced 
by  the  light  on  the  more  oblique  surfaces  of  ocular  glasses  of  short  focal 
lengths,  the  intensity  of  the  light  of  the  star  is  constant  as  long  as  the 
aperture  of  the  object-glass  does  not  vary.  As  we  have  already  seen, 
the  brightness  of  the  field  of  view,  on  the  contrary,  diminishes  inces- 
santly in  the  same  ratio  in  which  the  magnifying  power  increases.  All 
other  circumstances,  therefore,  being  equal,  a  star  will  be  more  or  less 
visible,  and  its  prominence  on  the  field  of  the  telescope  will  be  more 
or  less  marked,  in  proportion  to  the  magnifying  powers  we  employ." 
— Arago,  Manuscript  0/1847. 

I  will  further  add  the  following  passage  from  the  Annuaire  du  Bu- 
reau des  Long,  pour  1846  (Notices  Scient.  par  M.  Arago),  p.  381 : 

"  L'experience  a  montre  que  pour  le  commun  des  hommes,  deux 
espaces  eclaires  et  contigus  ne  se  distingueut  pas  1'un  de  Pautre,  a  inoius 
que  leurs  intensites  comparatives  ne  presentent,  au  minimum,  une  dif 
ference  de  •$$.  Quand  une  lunette  est  tournee  vers  le  firmament,  son 
champ  semble  nniformement  eclaire :  c'est  qu'  alors  il  existe,  dans  un 
plan  passant  par  le  foyer  et  perpendiculaire  a  1'axe  de  1'objectiC  un« 
image  indefinie  de  la  region  atmospherique  vers  laquelle  la  lunette  est 
dirigee.  Supposous  qu'un  astre.  c'est-a-dire  uu  objet  situe  bieii  au- 


72  COSMOS. 

while,  in  accordance  with  another  law,  they  influence  the 
aerial  space  on  which  the  fixed  star  is  projected.  The  tele- 
scope, by  separating,  as  it  were,  the  illuminated  particles  of 
air  surrounding  the  object-glass,  darkens  the  field  of  view, 
and  diminishes  the  intensity  of  its  illumination.  We  are  en- 
abled to  see,  however,  only  by  means  of  the  difference  be- 
tween the  light  of  the  fixed  star  and  of  the  aerial  field  or  the 
mass  of  air  which  surrounds  the  star  in  the  telescope.  Plan- 
etary disks  present  very  different  relations  from  the  simple 
ray  of  the  image  of  a  fixed  star ;  since,  like  the  aerial  field 
(fair  aerienne),  they  lose  in  intensity  of  light  by  dilatation 
in  the  magnifying  telescope.  It  must  be  further  observed, 
that  the  apparent  motion  of  the  fixed  star,  as  well  as  of  the 
planetary  disk,  is  increased  by  high  magnifying  powers. 
This  circumstance  may  facilitate  the  recognition  of  objects 
by  day,  in  instruments  whose  movements  are  not  regulated 
paralactically  by  clock-work,  so  as  to  follow  the  diurnal  mo- 
tion of  the  heavens.  Different  points  of  the  retina  are  suc- 
cessively excited.  "  Very  faint  shadows  are  not  observed," 
Arago  elsewhere  remarks,  "  until  we  can  give  them  motion." 

In  the  cloudless  sky  of  the  tropics,  during  the  driest  sea- 
son of  the  year,  I  have  frequently  been  able  to  find  the  pale 
disk  of  Jupiter  with  one  of  Dollond's  telescopes,  of  a  magni- 
fying power  of  only  95,  when  the  sun  was  already  from  15° 
to  18°  above  the  horizon.  The  diminished  intensity  of  the 
light  of  Jupiter  and  Saturn,  when  seen  by  day  in  the  great 
Berlin  refractor,  especially  when  contrasted  with  the  equally 
reflected  light  of  the  inferior  planets,  Venus  and  Mercury, 
frequently  excited  the  astonishment  of  Dr.  Galle.  Jupiter's 
delA  de  1'atmosphere,  se  trouve  dans  la  direction  de  la  lunette :  son 
image  ne  sera  visible  qu'autant  qu'elle  augmentera  de  ^Vi  au  moins, 
1'intensite  de  la  portion  de  1'image  focale  indifinie  de  1'atmosphere,  sur 
laquelle  sa  propre  image  limitfe  ira  se  placer.  Sans  cela  le  champ 
visuel  continuera  a  paraitre  partout  de  la  meme  intensity." 

"  Experience  has  shown  that,  in  ordinary  vision,  two  illuminated  and 
contiguous  spaces  can  not  be  distinguished  from  each  other  unless  their 
comparative  intensities  present  a  minimum  difference  of  inj-th.  When 
a  telescope  is  directed  toward  the  heavens,  its  field  of  view  appears 
uniformly  illumined:  there  then  exists  in  a  plane  passing  through  the 
focus,  and  perpendicular  to  the  axis  of  the  object-glass,  an  indefinite  im- 
age of  the  atmospheric  region  toward  which  the  instrument  is  pointed. 
If  we  suppose  a  star,  that  is  to  say,  an  object  very  far  beyond  the  atmos- 
phere, situated  in  the  direction  of  the  telescope,  its  image  will  not  be 
visible  except  it  exceed,  by  at  least  g^-th,  the  intensity  of  that  portion 
of  the  indefinite  focal  image  of  the  atmosphere  on  which  its  limited 
proper  image  is  thrown.  Otherwise  the  visual  field  will  continue  to 
appear  esery  where  of  the  same  intensity.  ' 


SCINTILLATION    OF    THE    STARS.  73 

occultations  have  occasionally  been  observed  by  daylight, 
with  the  aid  of  powerful  telescopes,  as  in  1792,tby  Flau- 
gergues,  and  in  1820,  by  Struve.  Argelander  (on  the  7th 
of  December,  1849,  at  Bonn)  distinctly  saw  three  of  the  sat 
ellites  of  Jupiter,  a  quarter  of  an  hour  after  sunrise,  with 
one  of  Fraunhofer's  five-feet  telescopes.  He  was  unable  to 
distinguish  the  fourth  ;  but,  subsequently,  this  and  the  other 
satellites  were  observed  emerging  from  the  dark  margin  of 
the  moon,  by  the  assistant  astronomer  Schmidt,  with  the 
eight-feet  heliometer.  The  determination  of  the  limits  of 
the  telescopic  visibility  of  small  stars  by  daylight,  in  differ- 
ent climates,  and  at  different  elevations  above  the  sea's  level, 
is  alike  interesting  in  an  optical  and  a  meteorological  point 
of  view. 

Among  the  remarkable  phenomena  whose  causes  have  been 
much  contested,  in  natural  as  well  as  in  telescopic  vision,  we 
must  reckon  the  nocturnal  scintillation  of  the  stars.  Accord- 
ing to  Arago's  investigations,  two  points  must  be  specially  dis- 
tinguished in  reference  to  this  phenomenon* — firstly,  change 

*  The  earliest  explanations  given  by  Arago  of  scintillation  occur  in 
the  appendix  to  the  4th  book  of  my  Voyage  avx  Regions  Equinoxialet, 
torn,  i.,  p.  623.  I  rejoice  that  I  am  able  to  enrich  this  section  on  nat- 
ural and  telescopic  vision  with  the  following  explanations,  which,  for 
the  reasons  already  assigned,  I  subjoin  in  the  original  text. 

Des  causes  de  la  scintillation  des  ttoiles. 


lation,  c'est  le  changement  de  couleur.  Ce  changement  est  beaucoup 
plus  frequent  que  1'observation  ordinaire  1'indique.  En  effet,  en  agi- 
tant  la  lunette,  on  transforme  1'image  dans  uue  ligne  ou  un  cercle,  et 
tous  les  points  de  cette  ligne  ou  de  ce  cercle  paraissent  de  couleure  dif- 
ferentes.  C'est  la  resultante  de  la  superposition  de  toutes  ces  images 
que  1'on  voit,  lorsqu'on  laisse  la  lunette  immobile.  Les  rayons  qui  so 
reunissent  au  foyer  d'une  lentille,  vibrent  d'accord  ou  en  disaccord, 
s'ajoutent  ou  se  detruisent,  suivant  que  les  couches  qu'ils  ont  traver- 
sees,  ont  telle  ou  telle  refringence.  L'ensemble  des  rayons  rouges  petit 
se  detruire  seul,  si  ceux  de  droite  et  de  gauche,  et  ceux  de  haut  et  de 
bas,  ont  traverse  des  milieux  inegalement  refringents.  Nous  avons  dit 
seul,  parceque  la  difference  de  refringence  qui  correspond  a  la  destruc 
tion  du  rayon  rouge,  n'est  pas  la  meme  que  cella  qui  amene  la  destruc- 
tion du  rayon  vert,  et  reciproquement.  Main  tenant,  si  des  rayons  rou  ges 
sont  detruits,  ce  qui  reste  sera  le  blanc  moins  le  rouge,  c'est-a-dire  du 
vert.  Si  le  vert  au  contraire  est  detruit  par  interference,  1'image  sera 
du  blanc  moins  le  vert,  c'est-a-dire  du  rouge.  Pour  expliquer  pourquoi 
les  planetes  a  grand  diametre  ne  scintillent  pas  ou  tres  peu,  il  faut  se 
rappeler  que  le  disque  peut  £tre  consider^  comme  une  aggregation 
d'^toiles  ou  de  petits  points  qui  scintillent  isol^ment;  mais  les  images 
de  differentes  couleurs  que  chacun  de  ces  points  pris  isol^ment  don- 
nerait,  empietant  les  unes  sur  les  autres,  formeraient  du  blanc.  Lors- 
qu'on place  un  diaphragme  ju  un  bouchou  perce  d'uii  trou  sur  1'objec- 
VOL  III.— D 


74  COSMOS. 

in  the  intensity  of  the  light,  from  a  sudden  decrease  to  perfect 
extinction  and  rekindling ;  secondly,  change  of  color.  Both 

tif  d'une  lunette,  les  etoiles  acquiere'nt  un  disque  entoure  d'une  serie 
d'anneaux  lumineux.  Si  1'on  enfonce  1'oculaire,  le  disque  de  1'eioilo 
augmente  de  diamctre,  et  il  se  produit  dans  son  centre  un  trou  obscur ; 
si  on  1'enfonce  davantage,  un  point  lumineux  se  substitue  au  point  noir. 
Un  nouvel  enfoncemeut  donne  naissance  a  un  centre  noir,  etc.  Pro 
nons  la  lunette  lorsque  le  centre  de  1'image  est  noir,  et  visons  a  uno 
£toile  qui  ne  sciatillo  pas :  le  centre  restera  noir,  comme  il  l'6tait  au- 
paravant.  Si  au  contraire  on  dirige  la  lunette  &  une  4toile  qui  scintille, 
on  verra  le  centre  de  1'image  lumineux  et  obscur  par  intermittence. 
Dans  la  position  ou  le  centre  de  1'image  est  occup6  par  un  point  lumi- 
neux, on  verra  ce  point  disparaltre  et  renaitre  successivement.  Cette 
disparition  ou  reapparition  du  point  central  est  la  preuve  directe  de 
I' interference  variable  des  rayons.  Pour  bien  concevoir  1'absence  de 
lumiere  au  centre  de  ces  images  dilatees,  il  faut  se  rappeler  quo  les 
rayons  regulierement  refractes  par  1'objectif  ne  se  reunisseut  et  ne  peu- 
vent  par  consequent  interferer  qu'au  foyer :  par  consequent  les  images 
dilatees  que  ces  rayons  peuvent  produire,  resteraient  toujours  pleines 
(sans  trou).  Si  dans  une  certaine  position  de  1'oculaire  un  trou  se  pre- 
sente  au  centre  de  1'image,  c'est  que  les  rayons  r6gulierement  refrac- 
ted inierferent  avec  des  rayons  diffractes  sur  les  bords  du  diaphragme 
circulaire.  Le  phenomene  n'est  pas  constant,  parceque  les  rayons  qui 
interferent  dans  un  certain  moment,  n'interferent  pas  un  instant  apres, 
lorsqu'ils  ont  traverse  des  couches  atmospheriques  dont  le  pouvoir  r6- 
fringent  a  varie.  On  trouve  dans  cette  experience  la  preuve  manifesto 
du  role  que  joue  dans  le  ph^nomene  de  la  scintillation  1'inegale  refran- 
gibilit^  des  couches  atmospheriques  traversees  par  les  rayons  dont  le 
faisceau  est  tres  etroit.  II  r^sulte  de  ces  considerations  que  1'explica- 
tion  des  scintillations  ne  pent  etre  rattachee  qu'aux  phenomenes  des 
interference*  lumineuses.  Les  rayons  des  etoiles,  apres  avoir  traverse 
nne  atmosphere  ou  il  existe  des  couches  in^galement  chaudes,  inegale- 
ment  denses,  inegalement  humides,  vont  se  reiinir  au  foyer  d'une  len- 
tille,  pour  y  former  des  images  d'intensite  et  de  couleurs  perp6tuelle- 
ment  changeantes,  c'est-£-dire  des  images  telles  que  la  scintillation  les 
presente.  II  y  a  aussi  scintillation  hors  du  foyer  des  lunettes.  Les  ex- 
plications proposers  par  Galileo,  Scaliger,  Kepler,  Descartes,  Hooke, 
Huygens,  Newton  et  John  Michell,  que  j'ai  examin6  dans  un  tnemoife 
presente  a  1'Institut  en  1840  (Comptes  Rcndus,  t.  x.,  p.  83),  sont  inad- 
missibles.  Thomas  Young,  auquel  nous  devons  les  premieres  lois  des 
interferences,  a  cru  inexplicable  le  phenomene  de  la  scintillation.  La 
faussete  de  1'ancienne  explication" par  des  vapeurs  qui  voltigent  et  d6- 
placent,  est  deja  prouvee  par  la  circonstance  que  nous  voyons  la  scin- 
tillation des  yeux,  ce  qui  supposerait  un  deplacement  d'une  minute. 
Les  ondulations  du  bord  du  soleil  sont  de  4"  a  5",  et  peut-etre  des  pie- 
ces qui  manquent,  done  encore  effet  de  1'interference  des  rayons." 

On  the  causes  of  the  scintillation  of  the  stars. 

"  The  most  remarkable  feature  in  the  phenomenon  of  the  stars'  scin- 
tillation is  their  change  of  color.  This  change  is  of  much  more  frequent 
occurrence  than  would  appear  from  ordinary  observation.  Indeed,  on 
shaking  the  telescope,  the  image  is  transformed  into  a  line  or  circle,  and 
nil  the  points  of  this  line  or  circle  appear  of  different  colors.  We  havo 
here  the  results  of  the  superposition  of  all  the  images  seen  when  the 
toleacope  is  at  rest.  The  rays  united  in  the  focus  of  a  leas  vibrate  in 


SCINTILLATION    OF   THE   STARS.  75 

these  alterations  are  more  intense  in  reality  than  they  appear 
to  the  naked  eye ;  for  when  the  several  points  of  the  retina 

harmony  or  at  variance  with  one  another,  and  increase  or  destroy  one 
another  according  to  the  various  degrees  of  refraction  of  the  strata 
through  which  they  have  passed.  The  whole  of  the  red  rays  alone  can 
destroy  ono  another,  if  the  rays  to  the  right  and  left,  above  and  below 
them,  have  passed  through  unequally  refracting  media.  We  have  used 
the  term  alone,  because  the  difference  of  refraction  necessary  to  destroy 
the  red  ray  is  not  the  same  as  that  which  is  able  to  destroy  the  green 
ray,  and  vice  versa.  Now,  if  the  red  rays  be  destroyed,  that  which  re- 
mains will  be  white  minus  red,  that  is  to  say,  green.  If  the  green,  on 
the  other  hand,  be  destroyed  by  interference,  the  image  will  be  white 
minus  green,  that  is  to  say,  red.  To  understand  why  planets  having  large 
diameters  should  be  subject  to  little  or  no  scintillation,  it  must  be  remem- 
bered that  the  disk  may  be  regarded  as  an  aggregation  of  stars  or  of 
small  points,  scintillating  independently  of  each  other,  while  the  images 
of  different  colors  presented  by  each  of  these  points  taken  alone  would 
impinge  upon  one  another  and  form  white.  If  we  place  a  diaphragm 
or  a  cork  pierced  with  a  hole  on  the  object-glass  of  a  telescope,  the 
stars  present  a  disk  surrounded  by  a  series  of  luminous  rings.  On  push- 
ing in  the  eye-piece,  the  disk  of  the  star  increases  in  diameter,  and  a 
dark  point  appears  in  its  center ;  when  the  eye-piece  is  made  to  recede 
still  further  into  the  instrument,  a  luminous  point  will  take  the  place  of 
the  dark  point.  On  causing  the  eye-piece  to  recede  still  further,  a 
black  center  will  be  observed.  If,  while  the  center  of  the  image  is 
black,  we  point  the  instrument  to  a  star  which  does  not  scintillate,  it 
will  remain  bkck  as  before.  If,  on  the  other  hand,  we  point  it  to  a  scin- 
tillating star,  we  shall  see  the  center  of  the  image  alternately  luminous 
and  dark.  In  the  position  in  which  the  center  of  the  image  is  occu- 
pied by  a  luminous  point,  we  shall  see  this  point  alternately  vanish  and 
reappear.  This  disappearance  and  reappearance  of  the  central  point 
is  a  direct  proof  of  the  variable  interference  of  the  rays.  In  order  to 
comprehend  the  absence  of  light  from  the  center  of  these  dilated  im- 
ages, we  must  remember  that  rays  regularly  refracted  by  the  object- 
glass  do  not  reunite,  and  can  not,  consequently,  interfere  except  in  the 
focus ;  thus  the  images  produced  by  these  rays  will  always  be  uniform 
and  without  a  central  point.  If,  in  a  certain  position  of  the  eye-piece, 
a  point  is  observed  in  the  center  of  the  image,  it  is  owing  to  the  inter- 
ference of  the  regularly  refracted  rays  with  the  rays  diffracted  on  the 
margins  of  the  circular  diaphragm.  The  phenomenon  is  not  constant, 
for  the  rays  which  interfere  at  one  moment  no  longer  do  so  in  the  next, 
after  they  have  passed  through  atmospheric  strata  possessing  a  varying 
power  of  refraction.  We  here  meet  with  a  manifest  proof  of  the  im- 
portant part  played  in  the  phenomenon  of  scintillation  by  the  unequal 
refrangibility  of  the  atmospheric  strata  traversed  by  rays  united  in  a 
very  narrow  pencil." 

"  It  follows  from  these  considerations  that  scintillation  mast  necessa- 
rily be  referred  to  the  phenomena  of  luminous  interferences  alone  The 
rays  emanating  from  the  stars,  after  traversing  an  atmosphere  composed 
of  strata  having  different  degrees  of  heat,  density,  and  humidity,  com- 
bine in  the  focus  of  a  lens,  where  they  form  images  perpetually  chang- 
ing in  intensity  and  color,  that  is  to  say,  the  images  presented  by  scin- 
tillation. There  is  another  form  of  scintillation,  independent  of  the  fo 
cus  of  the  telescope.  The  explanations  of  this  phenomenon  advanced 


76  COSMOS. 

are  once  excited,  they  retain  the  impression  of  light  which 
they  have  received,  so  that  the  disappearance,  obscuration 
and  change  of  color  in  a  star  are  not  perceived  by  us  to  their 
full  extent.  The  phenomenon  of  scintillation  is  more  striking- 
ly manifested  in  the  telescope  when  the  instrument  is  shaken, 
for  then  different  points  of  the  retina  are  successively  excited, 
and  colored  and  frequently  interrupted  rings  are  seen.  The 
principle  of  interference  explains  how  the  momentary  colored 
effulgence  of  a  star  may  be  followed  by  its  equally  instanta- 
neous disappearance  or  sudden  obscuration,  in  an  atmosphere 
composed  of  ever-changing  strata  of  different  temperatures, 
moisture,  and  density.  The  undulatory  theory  teaches  us 
generally  that  two  rays  of  light  (two  systems  of  waves)  em- 
anating from  one  source  (one  center  of  commotion),  destroy 
each  other  by  inequality  of  path  ;  that  the  light  of  one  ray 
added  to  the  light  of  the  other  produces  darkness.  When  the 
retardation  of  one  system  of  waves  in  reference  to  the  other 
amounts  to  an  odd  number  of  semi-undulations,  both  systems 
endeavor  to  impart  simultaneously  to  the  same  molecule  of 
ether  equal  but  opposite  velocities,  so  that  the  effect  of  their 
combination  is  to  produce  rest  in  the  molecule,  and  therefore 
darkness.  In  some  cases,  the  refrangibility  of  the  different 
strata  of  air  intersecting  the  rays  of  light  exerts  a  greater  in- 
fluence on  the  phenomenon  than  the  difference  in  length  of 
their  path.* 

The  intensity  of  scintillations  varies  considerably  in  the  dif- 
ferent fixed  stars,  and  does  not  seem  to  depend  solely  on  their 
altitude  and  apparent  magnitude,  but  also  on  the  nature  of 
their  own  light.  Some,  as  for  instancfe  Vega,  flicker  less  than 
Arcturus  and  Procyon.  The  absence  of  scintillation  in  plan- 
ets with  larger  disks  is  to  be  ascribed  to  compensation  and  to 
the  naturalizing  mixture  of  colors  proceeding  from  different 
points  of  the  disk.  The  disk  is  to  be  regarded  as  an  aggregate 

oy  Galileo,  Scaliger,  Kepler,  Descartes,  Hooke,  Huygens,  Newton,  and 
John  Michell,  which  I  examined  in  a  memoir  presented  to  the  Institute 
in  1840  (Comptes  Rendus,  t.  x.,  p.  83),  are  inadmissible.  Thomas 
Young,  to  whom  we  owe  the  discovery  of  the  first  laws  of  interference 
regarded  scintillation  as  an  inexplicable  phenomenon.  The  erroneous- 
ness  of  the  ancient  explanation,  which  supposes  that  vapors  ascend  and 
displace  one  another,  is  sufficiently  proved  by  the  circumstance  that  we 
see  scintillations  with  the  naked  eye,  which  presupposes  a  displace 
ment  of  a  minute.  The  undulations  of  the  margin  of  the  sun  are  from 
4"  to  5",  and  are  perhaps  owing  to  chasms  or  interruptions,  and  there- 
fore also  to  the  effect  of  interference  of  the  rays  of  light."  (Extrac/i 
from  Arago's  MSS.  of  1847.) 

*  See  Arago,  in  the  Annuaire  pour  1831   p.  1C8. 


SCINTILLATION    CP   THE    STARS.  77 

of  stars  which  naturally  compensate  for  the  light  destroyed 
by  interference,  and  again  combine  the  colored  rays  into  white 
light.  For  this  reason,  we  most  rarely  meet  with  traces  of 
scintillation  in  Jupiter  and  Saturn,  but  more  frequently  in 
Mercury  and  Venus,  for  the  apparent  diameters  of  the  disks 
of  these  last-named  planets  diminish  to  4"*4  and  9"'5.  The 
diameter  of  Mars  may  also  decrease  to  3"-3  at  its  conjunc- 
tion. In  the  serene  cold  winter  nights  of  the  temperate  zone, 
the  scintillation  increases  the  magnificent  impression  produced 
by  the  starry  heavens,  and  the  more  so  from  the  circumstance 
that,  seeing  stars  of  the  sixth  and  seventh  magnitude  flicker- 
ing in  various  directions,  we  are  led  to  imagine  that  we  per- 
ceive more  luminous  points  than  the  unaided  eye  is  actually 
capable  of  distinguishing.  Hence  the  popular  surprise  at  the 
few  thousand  stars  which  accurate  catalogues  indicate  as  vis- 
ible to  the  naked  eye  !  It  was  known  in  ancient  times  by 
the  Greek  astronomers  that  the  flickering  of  their  light  dis- 
tinguished the  fixed  stars  from  the  planets  ;  but  Aristotle,  in 
accordance  with  the  emanation  and  tangential  theory  of  vi- 
sion, to  which  he  adhered,  singularly  enough  ascribes  the  scin- 
tillation of  the  fixed  stars  merely  to  a  straining  of  the  eye. 
"  The  riveted  stars  (the  fixed  stars),"  says  he,*  "  sparkle,  but 
not  the  planets  ;  for  the  latter  are  so  near  that  the  eye  is  able 
to  reach  them ;  but  in  looking  at  the  fixed  stars  (rrpdf  6e  rouf 
fj,£VovTa$),  the  eye  acquires  a  tremulous  motion,  owing  to  the 
distance  and  the  effort." 

In  the  time  of  Galileo,  between  1572  and  1604 — an  epoch 
remarkable  for  great  celestial  events,  when  three  starsf  of 
greater  brightness  than  stars  of  the  first  magnitude  suddenly 
appeared,  one  of  which,  in  Cygnus,  remained  luminous  for 
twenty-one  years — Kepler's  attention  was  specially  directed 
to  scintillation  as  the  probable  criterion  of  the  non-planetary 
nature  of  a  celestial  body.  Although  well  versed  in  the  sci- 
ence of  optics,  in  its  then  imperfect  state,  he  was  unable  to 
rise  above  the  received  notion  of  moving  vapors.J  In  the 
Chinese  Records  of  the  newly  appeared  stars,  according  to 
the  great  collection  of  Ma-tuan-lin,  their  strong  scintillation 
is  occasionally  mentioned. 

The  more  equal  mixture  of  the  atmospheric  strata,  in  and 
near  the  tropics,  and  the  faintness  or  total  absence  of  scintil- 

*  Aristot.,  De  Ccelo,  ii.,  8,  p.  290,  Bekker. 
t  Cosmos,  vol.  ii.,  p.  326. 

t  Causa  scintillationis,  in  Kepler,  De  Stella  nova  in  pede  Serpcntara, 
1606,  cap.  xviii.,  p.  92-97. 


lation  of  the  fixed  stars  when  they  have  risen  12°  or  15° 
above  the  horizon,  give  the  vault  of  heaven  a  peculiar  char- 
acter of  mild  effulgence  and  repose.  I  have  already  referred 
in  many  of  iny  delineations  of  tropical  scenery  to  this  charac- 
teristic, which  was  also  noticed  by  the  accurate  observers  La 
Condamine  and  Bouguer,  in  the  Peruvian  plains,  and  by 
Garcin,*  in  Arabia,  India,  and  on  the  shores  of  the  Persian 
Gulf  (near  Bender  Abassi). 

As  the  aspect  of  the  starry  heavens,  in  the  season  of  the 
serene  and  cloudless  nights  of  the  tropics,  specially  excited 
my  admiration,  I  have  been  careful  to  note  in  my  journals 
the  height  above  the  horizon  at  which  the  scintillation  of  the 
stars  ceased  in  different  hygrometric  conditions.  Cumana 
and  the  rainless  portion  of  the  Peruvian  coast  of  the  Pacific, 
before  the  season  of  the  garua  (mist)  had  set  in,  were  pecul- 
iarly suited  to  such  observations.  On  an  average,  the  fixed 
stars  appear  only  to  scintillate  when  less  than  10°  or  12° 
above  the  horizon.  At  greater  elevations,  they  shed  a  mild, 
planetary  light;  but  this  difference  is  most  strikingly  per- 
ceived when  the  same  fixed  stars  are  watched  in  their  grad- 
ual rising  or  setting,  and  the  angles  of  their  altitudes  meas- 
ured or  calculated  by  the  known  time  and  latitude  of  the 
place.  In  some  serene  and  calm  nights,  the  region  of  scin- 
tillation extended  to  an  elevation  of  20°  or  even  25°  ;  but  a 
connection  could  scarcely  ever  be  traced  between  the  differ- 
ences of  altitude  or  intensity  of  the  scintillation  and  the  hy- 
grometric and  thermometric  conditions,  observable  in  the  low- 
er and  only  accessible  region  of  the  atmosphere.  I  have  ob- 
served, during  successive  nights,  after  considerable  scintilla- 
tion of  stars,  having  an  altitude  of  60°  or  70°,  when  Saus- 
sure's  hair-hygrometer  stood  at  85°,  that  the  scintillation  en- 
tirely ceased  when  the  stars  were  15°  above  the  horizon,  al- 
though the  moisture  of  the  atmosphere  was  so  considerably 
increased  that  the  hygrometer  had  risen  to  93°.  The  intri- 
cate compensatory  phenomena  of  interference  of  the  rays  of 
light  are  modified,  not  by  the  quantity  of  aqueous  vapor  con- 
tained in  solution  in  the  atmosphere,  but  by  the  unequal  dis- 
tribution of  vapors  in  the  superimposed  strata,  and  by  the 
upper  currents  of  cold  and  warm  air,  which  are  not  percept- 
ible in  the  lower  regions  of  the  atmosphere.  The  scintilla- 
tion of  stars  at  a  great  altitude  was  also  strikingly  increased 
during  the  thin  yellowish  red  mist  which  tinges  the  heavens 

*  Lettre  de  M.  Garcin,  Dr.  en  Med.  a  M.  de  RSavmur,  in  Hist,  de 
TAcadtmie  Royale  des  Sciences,'  Annie  1743,  p.  28-32. 


SCINTILLATION    OF   THE    STARS.  79 

Bhort\y  before  an  earthquake.  These  observations  only  refer 
to  the  serenely  bright  and  rainless  seasons  of  the  year  with- 
in the  tropics,  from  10°  to  12°  north  and  south  of  the  equa- 
tor. The  phenomena  of  light  exhibited  at  the  commence- 
ment of  the  rainy  season,  during  the  sun's  zenith-passage, 
depend  on  very  general,  yet  powerful,  and  almost  tempestu- 
ous causes.  The  sudden  decrease  of  the  northeast  trade- wind, 
and  the  interruption  of  the  passage  of  regular  upper  currents 
from  the  equator  to  the  poles,  and  of  lower  currents  from  the 
poles  to  the  equator,  generate  clouds,  and  thus  daily  give  rise, 
at  definite  recurring  periods,  to  storms  of  wind  and  torrents 
of  rain.  I  have  observed  during  several  successive  years 
that  in  regions  where  the  scintillation  of  the  fixed  stars  is 
of  rare  occurrence,  the  approach  of  the  rainy  season  is  an- 
nounced many  days  beforehand  by  a  flickering  light  of  the 
stars  at  great  altitudes  above  the  horizon.  This  phenome- 
non is  accompanied  by  sheet  lightning,  and  single  flashes  on 
the  distant  horizon,  sometimes  without  any  visible  cloud,  and 
at  others  darting  through  narrow,  vertically  ascending  col- 
umns of  clouds.  In  several  of  my  writings  I  have  endeav- 
ored to  delineate  these  precursory  characteristics  and  physi- 
ognomical changes  in  the  atmosphere.* 

The  second  book  of  Lord  Bacon's  Novum  Organum  gives 
us  the  earliest  views  on  the  velocity  of  light  and  the  prob- 
ability of  its  requiring  a  certain  time  for  its  transmission. 
He  speaks  of  the  time  required  by  a  ray  of  light  to  traverse 
the  enormous  distances  of  the  universe,  and  proposes  the 

*  See  Voyage  aux  Regions  Equin.,  t.  i.,  p.  511  and  512,  and  t.  ii.,  p. 
202-208;  also  my  Views  of  Nature,  p.  16,  138. 

En  Arabie,  de  meme  qu'a  Bender-Abassi,  port  fameux  du  Golfe 


Persique,  1'air  est  parfaitement  serein  presque  toute  1'annee.  Le  prin- 
temps,  l'et£,  et  1'automne  se  passent,  sans  qu'on  y  voie  la  moindre  rosee. 
Dans  ces  raemes  temps  tout  le  monde  couche  dehors  sur  le  haut  dea 
maisons.  Quand  on  est  ainsi  couche,  il  n'est  pas  possible  d'exprimer  le 
plaisir  qu'on  prend  4  contempler  la  beaute  du  ciel,  1'eclat  des  etoiles. 
C'est  une  lumiere  pure,  ferme  et  eclatante,  sans  4tincellement.  Ce  n'est 
qu'au  milieu  de  1'hiver  que  la  scintillation,  quoique  tres  foible,  s'y  fait 
apercevoir." 

"  In  Arabia,"  says  Garciu,  "as  also  at  Bender-Abassi,  a  celebrated 
port  on  the  Persian  Gulf,  the  air  is  perfectly  serene  throughout  nearly 
the  whole  of  the  year.  Spring,  summer,  and  autumn  pass  without  ex- 
hibiting a  trace  of  dew.  During  these  seasons  all  the  inhabitants  sleep 
on  the  roofs  of  their  houses.  It  is  impossible  to  describe  the  pleasure 
experienced  in  contemplating  the  beauty  of  the  sky,  and  the  brightness 
of  the  stars,  while  thus  lying  in  the  open  air.  The  light  of  the  stars  is 
pure,  steady,  and  brilliant ;  and  it  is  only  in  the  middle  of  the  winter 
that  a  slight  degree  of  scintillation  is  observed." — Garcin,  in  Hist,  dt 
PAcad.  de*  Sc.,  1743,  p.  30. 


80  COSMOS. 

question  whether  those  stars  yet  exist  which  we  now  see 
shining.*  We  are  astonished  to  meet  with  this  happy  con- 
jecture in  a  work  whose  intellectual  author  was  far  behind 
his  cotemporaries  in  mathematical,  astronomical,  and  phys- 
ical knowledge.  The  velocity  of  reflected  solar  light  was 
first  measured  by  Homer  (November,  1675)  by  comparing 
the  periods  of  occultation  of  Jupiter's  satellites  ;  while  the 
velocity  of  the  direct  light  of  the  fixed  stars  was  ascertained 
(in  the  autumn  of  1727)  by  means  of  Bradley's  great  discov- 
ery of  aberration,  which  afforded  objective  evidence  of  the 
translatory  movement  of  the  earth,  and  of  the  truth  of  the 
Copernican  system.  In  recent  times,  a  third  method  of 
measurement  has  been  suggested  by  Arago,  which  is  based 
on  the  phenomena  of  light  observed  in  a  variable  star,  as, 
for  instance,  Algol  in  Perseus. f  To  these  astronomical  meth- 
ods may  be  added  one  of  terrestrial  measurement,  lately  con- 
ducted with  much  ingenuity  and  success  by  M.  Fizeau  in 
the  neighborhood  of  Paris.  It  reminds  us  of  Galileo's  early 

*  In  speaking  of  the  deceptions  occasioned  by  the  velocity  of  sound 
and  light,  Bacon  says :  "  This  last  instance,  and  others  of  a  like  nature, 
have  sometimes  excited  in  us  a  most  marvelous  doubt,  no  less  than 
•whether  the  image  of  the  sky  and  stars  is  percei  ved  as  at  the  actual 
moment  of  its  existence,  or  rather  a  little  after,  and  whether  there  is  not 
(with  regard  to  the  visible  appearance  of  the  heavenly  bodies)  a  true 
and  apparent  place  which  is  observed  by  astronomers  in  parallaxes.  It 
appeared  so  incredible  to  us  that  the  images  or  radiations  of  heavenly 
bodies  could  suddenly  be  conveyed  through  such  immense  spaces  to  the 
eight,  and  it  seemed  that  they  ought  rather  to  be  transmitted  in  a  def- 
inite time.  That  doubt,  however,  as  far  as  regards  any  great  difference 
between  the  true  and  apparent  time,  was  subsequently  completely  set 
at  rest  when  we  considered  .  .  .  ." — The  works  of  Francis  Bacon,  vol. 
xiv.,  Lond.,  1831  (Novum  Organutn),  p.  177.  He  then  recalls  the  cor- 
rect view  he  had  previously  announced  precisely  in  the  manner  of  the 
ancients.  Compare  Mrs.  Somerville's  Connection  of  the  Physical  Sci- 
ences, p.  36,  and  Cosmos,  vol.  i.,  p.  154,  155. 

t  See  Arago's  explanation  of  his  method  in  the  Annuaire  du  Bureau 
des  Longitudes  pour  1842,  p.  337-343.  "  L'observation  attentive  des 
phases  d'Algol  i  six  mois  d'intervalle  servira  a  determiner  directement 
la  vitesse  de  la  lumiere  de  cette  etoile.  Pres  du  maximum  et  du  mini- 
mum le  changement  d'intensite  s'opere  lentement ;  il  est  au  contraire 
rapide  a  certames  epoques  interme'diares  entre  celles  qui  correspondent 
aux  deux  etats  extremes,  quand  Algol,  soil  en  diminuant,  soit  en  aug- 
mentant  d'dclat,  passe  pour  la  troisieme  grandeur." 

"  The  attentive  observation  of  the  phases  of  Algol  at  a  six-months  in- 
terval will  serve  to  determine  directly  the  velocity  of  that  star's  light 
Near  the  maximum  and  the  minimum  the  change  of  intensity  is  very 
slow ;  it  is,  on  the  contrary,  rapid  at  certain  intermediate  epochs  be- 
tween those  corresponding  to  the  two  extremes,  when  Algol,  either  di 
minishing  or  increasing  in  Brightness,  appears  of  the  third  magnitude. 


SCINTILLATION    OF   THE    STARS.  81 

and  fruitless  experiments  with  two  alternately  obscured  lan- 
terns. 

Horrebow  and  Du  Hamel  estimated  the  time  occupied  in 
the  passage  of  light  from  the  sun  to  the  earth  at  its  mean  dis- 
tance, according  to  Romer's  first  observations  of  Jupiter's  satel- 
lites, at  14'  7",  then  11' ;  Cassini  at  14'  10" ;  while  Newton* 

*  Newton,  Optics,  2d  ed.  (London,  1718),  p.  325.  "  Light  moves 
from  the  sun  to  us  in  seven  or  eight  minutes  of  time."  Newton  com- 
pares the  velocity  of  sound  (1140  feet  in  1")  with  that  of  light.  As, 
from  observations  on  the  occultations  of  Jupiter's  satellites  (Newton's 
death  occurred  about  half  a  year  before  Bradley's  discovery  of  aberra- 
tion), he  calculates  that  light  passes  from  the  sun  to  the  earth,  a  distance, 
as  he  assumed,  of  70  millions  of  miles,  in  7'  30" ;  this  result  yields  a  ve- 
locity of  light  equal  to  155,555|  miles  in  a  second.  The  reduction  of 
these  [ordinary]  to  geographical  miles  (60  to  1°)  is  subject  to  variations 
according  as  we  assume  the  figure  of  the  earth.  According  to  Encke's 
accurate  calculations  in  the  Jahrbuch  fur  1852,  an  equatorial  degree  is 
equal  to  69-1637  English  miles.  According  to  Newton's  data,  we  should 
therefore  have  a  velocity  of  134,944  geographical  miles.  Newton,  how- 
ever, assumed  the  sun's  parallax  to  be  12".  If  this,  according  to  Encke's 
calculation  of  the  transit  of  Venus,  be  8"-57116,  the  distance  is  greater, 
and  we  obtain  for  the  velocity  of  light  (at  seven  and  a  half  minutes) 
188,928  geographical,  or  217,783  ordinary  miles,  in  a  second  of  time  ; 
therefore  too  much,  as  before  we  had  too  h'ttle.  It  is  certainly  very  re- 
markable, although  the  circumstance  has  been  overlooked  by  Delambre 
(Hist,  de  V Astronomic  Moderne,  torn,  ii.,  p.  653),  that  Newton  (proba- 
bly basing  his  calculations  upon  more  recent  English  observations  of 
the  first  satellite)  should  have  approximated  within  47"  to  the  true  re- 
sult (namely,  that  of  Struve,  which  is  now  generally  adopted),  while 
the  time  assigned  for  the  passage  of  light  over  the  semi-diameter  of  the 
earth's  orbit  continued  to  vacillate  between  the  very  high  amounts  of 
11'  and  14'  10",  from  the  period  of  Earner's  discovery  in  1675  to  the  be- 
ginning of  the  eighteenth  century.  The  first  treatise  in  which  RSmer, 
the  pupil  of  Picard,  communicated  his  discovery  to  the  Academy,  bears 
the  date  of  November  22,  1675.  He  found,  from  observations  of  forty 
emersions  and  immersions  of  Jupiter's  satellites,  "a  retardation  of  light 
amounting  to  22  minutes  for  an  interval  of  space  double  that  of  the  sun's 
distance  from  the  earth."  (Memoirs  de  VAcad.  de  1666-1699,  torn,  x., 
1730,  p.  400.)  Cassini  does  not  deny  the  retardation, but  he  does  not 
concur  in  the  amount  of  time  given,  because,  as  he  erroneously  argues, 
different  satellites  presented  different  results.  Du  Hamel,  secretary  to 
the  Paris  Academy  (Regies  Scientiarum  Academics  Historia,  1698,  p. 
143),  gave  from  10  to  11  minutes,  seventeen  years  after  RSmer  had  left 
Pans,  although  he  refers  to  him ;  yet  we  know,  through  Peter  Horre- 
bow (Basis  Astronomic  sive  Trvluum  Roemerianum,  1735,  p.  122-129), 
that  Romer  adhered  to  the  result  of  11',  when  in  1704,  six  years  before 
his  death,  he  purposed  bringing  out  a  work  on  the  velocity  of  light; 
the  same  was  the  case  with  Huygens  (Tract,  de  Lumine,  cap.  i.,  p.  7) 
Cassini's  method  was  very  different ;  he  found  7'  5"  for  the  first  satel- 
lite, and  14'  12"  for  the  second,  having  taken  14'  10"  for  the  basis  of 
his  tables  for  Jupiter  pro  pcragrando  diametri  semissi.  The  error  waa 
therefore  on  the  increase.  (Compare  Horrebow,  Triduum,  p.  129  ;  Gas- 
sini,  Hypotheses  et  Satellites  de  Jupiter  iu  the  M6m  de  VAcad.,  166G- 

D  2 


82  COSMOS. 

approximated  very  remarkably  to  the  truth  when  he  gave 
it  at  7'  30".  Delambre,*  who  did  not  take  into  account  any 
of  the  observations  made  in  his  own  time,  with  the  excep- 
tion of  those  of  the  first  satellite,  found  8'  13"-2.  Encke 
has  very  justly  noticed  the  great  importance  of  undertaking 
a  special  course  of  observations  on  the  occultations  of  Jupi- 
ter's satellites,  in  order  to  arrive  at  a  correct  idea  regarding 
the  velocity  of  light,  now  that  the  perfection  attained  in  the 
construction  of  telescopes  warrants  us  in  hoping  that  we  may 
obtain  trustworthy  results. 

Dr.  Busch,t  of  Konigsberg,  who  based  his  calculations  on 
Bradley's  observations  of  aberration,  as  rediscovered  by  Bi- 
gaud  of  Oxford,  estimated  the  passage  of  light  from  the  sun 
to  the  earth  at  8'  12"- 14,  the  velocity  of  stellar  light  at 
167,976  miles  in  a  second,  and  the  constant  of  aberration 
at  20"-2116  ;  but  it  would  appear,  from  the  more  recent  ob- 
servations on  aberration  carried  on  during  eighteen  months 
by  Struve  with  the  great  transit  instrument  at  Pulkowa,t 
that  the  former  of  these  numbers  should  be  considerably  in- 

1699,  torn,  viii.,  p.  435,  475;  Delambre,  Hist,  de  VAstr.  Mod.,  toin.  ii., 
p.  751, 782 ;  Du  Hamel,  Physica,  p.  435.) 

*  Delambre,  Hist,  de  VAstr.  Mod.,  torn,  ii.,  p.  653. 

t  Reduction  of  Bradley's  Observations  at  Kew  and  Wangled,  1836,  p. 
22;  Schumacher's  Astr.  Nachr.,  bd.  xiii.,  1836,  No.  309  (compare  Mis- 
cellaneous Works  and  Correspondence  of  the  Rev.  James  Bradley,  by 
Prof.  Rigaud,  Oxford,  1832).  On  the  mode  adopted  for  explaining  ab- 
erration in  accordance  with  the  theory  of  undulatory  light,  see  Doppler, 
in  iheAbhl.  derKon.  bohmischen  Gesellschaft  der  Wiss.,5te  Folge.,  bd. 
iii.,  s.  754-765.  It  is  a  point  of  extreme  importance  in  the  history  of 
great  astronomical  discoveries,  that  Picard,  more  than  half  a  century 
before  the  actual  discovery  and  explanation  by  Bradley  of  the  cause 
of  aberration,  probably  from  1667,  had  observed  a  periodical  movement 
of  the  polar  star  to  the  extent  of  about  20",  which  could  "  neither  be 
the  effect  of  parallax  or  of  refraction,  and  was  very  regular  at  opposite 
seasons  of  the  year."  (Delambre,  Hist,  de  I' Astr.  Moderns,  torn,  ii.,  p. 
616.)  Picard  had  nearly  ascertained  the  velocity  of  direct  light  before 
his  pupil,  R6mer,  made  known  that  of  reflected  light. 

\  Schum.,  Astr.  Nachr  , bd.  xxi.,  1844,  No.  484 ;  Struve,  Eludes  d'Astr. 
Stellaire,  p.  103,  107  (compare  Cosmos,  vol.  i.,  p.  153,  154).  The  re- 
suit  given  in  the  Annuaire  pour  1842,  p  87,  for  the  velocity  of  light 
in  a  second,  is  308,000  kilomenes,  or  77,000  leagues  (each  of  4000 
metres),  which  corresponds  to  215,834  miles,  and  approximates  most 
nearly  to  Struve's  recent  result,  while  that  obtained  at  the  Pulkowa 
Observatory  is  189,746  miles.  On  the  difference  in  the  aberration  of 
the  light  01  the  polar  star  and  that  of  its  companion,  and  on  the  doubts 
recently  expressed  by  Struve,  see  Madler,  Astronomic,  1849,  s.  393. 
William  Richardson  gives  as  the  result  of  the  passage  of  light  from  the 
Bun  to  the  earth  8'  19"-28,  from  which  we  obtain  a  velocity  of  215,392 
milei  in  a  second.  (Mem.  of  the  Astren.  Soc.,  vol.  iv.,  Part  i..  p.  68.) 


SCINTILLATION    OF    THE    STARS.  83 

creased.  The  result  of  these  important  observations  gave 
8'  17"'78  ;  from  which,  with  a  constant  of  aberration  of 
20"-4451,  and  Encke's  correction  of  the  sun's  parallax  in  the 
year  1835,  together  with  his  determination  of  the  earth's 
radius,  as  given  in  his  Astronomisches  Jahrbuch  fur  1852, 
we  obtain  166,196  geographical  miles  for  the  velocity  of 
light  in  a  second.  The  probable  error  in  the  velocity  seems 
scarcely  to  amount  to  eight  geographical  miles.  Struve's 
result  for  the  time  which  light  requires  to  pass  from  the  sun 
to  the  earth  differs  about  7TTrth  from  Delambre's  (8'  13"'2), 
which  has  been  adopted  by  Bessel  in  the  Tab.  Regiom.,  and 
has  hitherto  been  followed  in  the  Berlin  Astronomical  Al- 
manac. The  discussion  on  this  subject  can  not,  however, 
be  regarded  as  wholly  at  rest.  Great  doubts  still  exist  as 
to  the  earlier  adopted  conjecture  that  the  velocity  of  the 
light  of  the  polar  star  was  smaller  than  that  of  its  compan- 
ion in  the  ratio  of  133  to  134. 

M.  Fizeau,  a  physicist,  distinguished  alike  for  his  great 
acquirements  and  for  the  delicacy  of  his  experiments,  has 
submitted  the  velocity  of  light  to  a  terrestrial  measurement, 
by  means  of  an  ingeniously  constructed  apparatus,  in  which 
artificial  light  (resembling  stellar  light)  generated  from  oxy- 
gen and  hydrogen  is  made  to  pass  back,  by  means  of  a  mir- 
ror between  Suresne  and  La  Butte  Montmartre,  over  a  dis- 
tance of  28,321  feet,  to  the  same  point  from  which  it  ema- 
nated. A  disk  having  720  teeth,  which  made  12-6  rotations 
in  a  second,  alternately  obscured  the  ray  of  light  and  allowed 
it  to  be  seen  between  the  teeth  on  the  margin.  It  was  sup- 
posed from  the  marking  of  a  counter  (compteur)  that  the 
artificial  light  traversed  56,642  feet,  or  the  distance  to  and 
from  the  stations  in  T^7?th  part  of  a  second,  whence  we  ob- 
tain a  velocity  of  191,460  miles  in  a  second.*  This  result, 
therefore,  approximates  most  closely  to  Delambre's  (which 
was  189,173  miles),  as  obtained  from  Jupiter's  satellites. 

Direct  observations  and  ingenious  reflections  on  the  ab- 
sence of  all  coloration  during  the  alternation  of  light  in  the 
variable  stars — a  subject  to  which  I  shall  revert  in  the  se- 

*  Fizean  gives  his  result  in  leagues,  reckoning  25  (and  consequently 
4452  metres)  to  the  equatorial  degree.  He  estimates  the  velocity  of 
light  at  70,000  such  leagues,  or  about  210,000  miles  in  the  second.  On 
the  earlier  experiments  of  Fizeau,  see  Comptes  Rendvt,  torn,  xxix.,  p.  92. 
In  Moigno,  Rupert.  tfOptique  Moderne,  Part  iii.,  p.  1162,  we  find  this 
velocity  given  at  70,843  leagues  (of  25=1°),  or  about  212,529  miles, 
which  approximates  most  nearly  to  the  result  of  Bradley,  as  given  by 
Busch. 


84  COSMOS. 

quel — led  Arago  to  the  result  that,  according  to  the  undu- 
latory  theory,  rays  of  light  of  different  color,  which  conse 
quently  have  transverse  vibrations  of  very  different  length 
and  velocity,  move  through  space  with  the  same  rapidity. 
The  velocity  of  transmission  and  refraction  differ,  therefore, 
in  the  interior  of  the  different  bodies  through  which  the  col- 
ored rays  pass  ;*  for  Arago's  observations  have  shown  that 

*  "  D'apres  la  theorie  mathematique  dans  le  systeme  des  ondes,  les 
rayons  de  differentes  couleurs,  les  rayons  dont  les  ondulations  sont  ine- 
gales,  doivent  neanmoins  se  propager  dans  I'ether  avec  la  meme  vi- 
tesse.  H  n'y  a  pas  de  difference  a  cet  egard  entre  la  propagation  des 
ondes  sonores,  lesquelles  se  propagent  dans  1'air  avec  la  memo  rapidite. 
Cette  6galit6  de  propagation  des  ondes  sonores  est  bien  etablio  experi- 
mentalement  par  la  similitude  d'effet  que  produit  une  musique  donnee 
&  toutes  distances  du  lieu  ou  1'on  1'execute.  La  principale  difficulte, 
je  dirai  1'unique  difficulte,  qu'on  cut  elev6e  contre  le  systeme  des  ondes, 
consistait  done  a  expliquer,  comment  la  vitesse  de  propagation  des  ray- 
ons de  differentes  couleurs  dans  les  corps  differents  pouvait  etre  dissem- 
blable  et  servir  a  rendre  compte  de  1'inegalite  de  refraction  de  ces  ray- 
ons ou  de  la  dispersion.  On  a  montre  r6cemment  que  cette  difBculte 
n'est  pas  insurmontable ;  qu'on  peut  constituer  I'ether  dans  les  corps 
inegalement  denses  de  maniere  que  des  rayons  a  ondulations  dissem- 
blables  s'y  propagent  avec  des  vitesses  inegales :  reste  a  determiner,  si 
les  conceptions  des  geometres  a  cet  egard  sont  conformes  a  la  nature 
des  choses.  Voici  les  amplitudes  des  ondulations  deduites  experimen- 
talement  d'une  serie  de  fails  relatif  aux  interferences : 

mm. 

Violet 0-000423 

Jaune 0-000551 

Rouge 0-000620 

La  vitesse  de  transmission  des  rayons  de  diffe>entes  couleurs  dans  le» 
espaces  celestes  est  la  meme  dans  le  systeme  des  ondes  et  tout-a-fait 
Ind^pendante  de  1'etendue  ou  de  la  vitesse  des  ondulations." 

"  According  to  the  mathematical  theory  of  a  system  of  waves,  rayi 
of  different  colors,  having  unequal  undulations,  must  nevertheless  be 
transmitted  through  ether  with  the  same  velocity.  There  is  no  differ- 
ence hi  this  respect  from  the  mode  of  propagation  of  waves  of  sound 
which  are  transmitted  through  the  atmosphere  with  equal  velocity. 
This  equality  of  transmission  in  waves  of  sound  may  be  well  demon 
strated  experimentally  by  the  uniformity  of  effect  produced  by  music 
at  all  distances  from  the  source  whence  it  emanates.  The  principal,  I 
may  say  the  only  objection,  advanced  against  the  undulatory  theory, 
consisted  in  the  difficulty  of  explaining  how  the  velocity  of  the  propa- 
gation of  rays  of  different  colors  through  different  bodies  could  be  dis 
similar,  while  it  accounted  for  the  inequality  of  thd  "^fraction  of  the 
rays  or  of  their  dispersion.  It  has  been  recently  shown*  that  this  diffi 
culty  is  not  insurmountable,  and  that  the  ether  may  be  supposed  to  bo 
transmitted  through  bodies  of  unequal  density  in  such  a  manner  that 
rays  of  dissimilar  systems  of  waves  may  be  propagated  through  it  with 
unequal  velocities ;  but  it  remains  to  be  determined  whether  the  views 
advanced  by  geometricians  on  this  question  are  in  unison  with  the  act- 
ual nature  of  things.  The  following  are  the  lengths  of  the  undulations 


VELOCITY    OF   LIGHT.  85 

refraction  in  the  prism  is  not  altered  by  the  relation  of  the 
velocity  of  light  to  that  of  the  earth's  motion.  All  the  meas- 
urements coincide  in  the  result,  that  the  light  of  those  stars 
toward  which  the  earth  is  moving  presents  the  same  index 
of  refraction  as  the  light  of  those  from  which  it  is  receding. 
Using  the  language  of  the  emission  hypothesis,  this  celebra- 
ted observer  remarks,  that  bodies  send  forth  rays  of  all  ve- 
locities, but  that  among  these  different  velocities  one  only 
is  capable  of  exciting  the  sensation  of  light.* 

as  experimentally  deduced  from  a  series  of  facts  in  relation  to  inter- 
ference : 

mm. 

Violet 0-000423 

Yellow 0-000551 

Red 0-000620 

The  velocity  of  the  transmission  of  rajs  of  different  colors  through  ce- 
lestial space  is  equal  in  the  system  of  waves,  and  is  quite  independent 
of  the  length  or  the  velocity  of  the  undulations." — Arago,  MS.  of  1849. 
Compare  also  the  Annuaire  pour  1842,  p.  333-336.  The  length  of  the 
luminous  wave  of  the  ether,  and  the  velocity  of  the  vibrations,  determ- 
ine the  character  of  the  colored  rays.  To  the  violet,  which  is  the  most 
refrangible  ray,  belong  662,  while  to  the  red  (or  least  refrangible  ray 
with  the  greatest  length  of  wave)  there  belong  451  billions  of  vibra- 
tions in  the  second. 

*  "  J'ai  prouve,  il  y  a  bien  des  annees,  par  des  observations  directes 
que  les  rayons  des  Stoiles  vers  lesquelles  la  Terre  marche,  et  les  ray- 
ons des  etoiles  dont  la  terre  s'eloigne,  se  refractent  exactement  de  la 
meme  quantite.  Un  tel  resultat  ne  pent  se  concilier  avec  la  tkforie  de 
remission  qu'a  1'aide  d'une  addition  importante  a  faire  a  cette  theorie : 
il  faut  admettre  que  les  corps  lumineux  emettent  des  rayons  de  toutes 
les  vitesses,  et  que  les  seuls  rayons  d'une  vitesse  determined  sont  visi- 
bles,  qu'eux  seuls  produisent  dans  Tcei!  la  sensation  de  lumiere.  Dans 
la  theorie  de  1'emission,  le  rouge,  le  jaune,  le  vert,  le  bleu,  le  violet  so- 
laires  sont  respectivement  accompagnes  de  rayons  pareils,  mais  obscurs 
par  defaut  ou  par  exces  de  vitesse.  A  plus  de  vitesse  correspond  une 
moindre  refraction,  comtne  moins  de  vitesse  entraine  une  refraction  plus 
grande.  Ainsi  chaque  rayon  rouge  visible  est  accompagne  de  rayons 
obscurs  de  la  meme  nature,  qui  se  refractent  les  uns  plus,  les  autres 
moins  que  lui :  ainsi  il  existe  des  rayons  dans  les  stries  noiret  de  la  por- 
tion rouge  du  spectre ;  la  meme  chose  doit  etre  admise  des  stries  situ 
ees  dans  les  portions  jaunes,  vertes,  bleues  et  violettes." 

"  I  showed  many  years  ago,  by  direct  observations,  that  the  rays  of 
those  stars  toward  which  the  earth  moves,  and  the  rays  of  those  stars 
from  which  it  recedes,  are  repeated  in  exactly  the  same  degree.  Such 
a  result  can  not  be  reconciled  with  the  theory  of  emistion,  unless  we 
make  the  important  admission  that  luminous  bodies  emit  rays  of  all  ve- 
locities, and  that  only  rays  of  a  determined  velocity  are  visible,  these 
alone  being  capable  of  impressing  the  eye  with  the  sensation  of  light. 
In  the  theory  of  emission,  the  red,  yellow,  green,  blue,  and  violet  so- 
lar rays  are  respectively  accompanied  by  like  rays,  which  are,  how- 
ever, dark  from  deficiency  or  excess  of  velocity.  Excessive  velocity  is 


86  COSMOS. 

On  comparing  the  velocities  of  solar,  stellar,  and  terres- 
trial light,  which  are  all  equally  refracted  in  the  prism, 
with  the  velocity  of  th&  light  of  frictional  electricity,  we  are 
disposed,  in  accordance  with  Wheatstone's  ingeniously  con- 
ducted experiments,  to  regard  the  lowest  ratio  in  which  the 
latter  exceeds  the  former  as  3  :  2.  According  to  the  lowest 
results  of  Wheatstone's  optical  rotatory  apparatus,  electric 
light  traverses  288,000  miles  in  a  second.*  If  we  reckon 
189,938  miles  for  stellar  light,  according  to  Struve's  observ- 
ations on  aberration,  we  obtain  the  difference  of  95,776  miles 
as  the  greater  velocity  of  electricity  in  one  second. 

These  results  are  apparently  opposed  to  the  views  ad- 
vanced by  Sir  William  Herschel,  according  to  which  solar 
and  stellar  light  are  regarded  as  the  effects  of  an  electro- 
magnetic process — a  perpetual  northern  light.  I  say  ap- 
parently, for  no  one  will  contest  the  possibility  that  there 
may  be  several  very  different  magneto-electrical  processes  in 
the  luminous  cosmical  bodies,  in  which  light — the  product 
of  the  process — may  possess  a  different  velocity  of  propaga 
tion.  To  this  conjecture  may  be  added  the  uncertainty  of 
the  numerical  result  yielded  by  the  experiments  of  Wheat- 
stone,  who  has  himself  admitted  that  they  are  not  sufficient- 
ly established,  but  need  further  confirmation  before  they  can 

associated  with  a  slight  degree  of  refraction,  while  a  smaller  amount  of 
velocity  involves  a  slighter  degree  of  refraction.  Thus  every  visible 
red  ray  is  accompanied  by  dark  rays  of  the  same  nature,  of  which  some 
are  more,  and  others  less,  refracted  than  the  former ;  there  are  conse- 
quently rays  in  the  black  lines  of  the  red  portion  of  the  spectrum ;  and 
the  same  must  be  admitted  in  reference  to  the  lines  situated  in  the  yel 
low,  green,  blue,  and  violet  portions." — Arago,  in  the  Comptes  Rendus 
de  VAcad.  des  Sciences,  t.  xvi.,  1843,  p.  404.  Compare  also  t.  viii.,  1839, 
p.  326,  and  Poisson,  Traite  de  Mccanique,  ed.  ii.,  1833,  t.  i.,  $  168.  Ac- 
cording to  the  undulatory  theory,  the  stars  emit  waves  of  extremely 
various  transverse  velocities  of  oscillations. 

*  Wheatstone,  in  the  Philos.  Transact,  of  the  Royal  Soc.for  1834,  p. 
589,  591.  From  the  experiments  described  in  this  paper,  it  would  ap 
pear  that  the  human  eve  is  capable  of  perceiving  phenomena  of  light, 
whose  duration  is  limited  to  the  millionth  part  of  a  second  (p.  591). 
On  the  hypothesis  referred  to  in  the  text,  of  the  supposed  analogy  be- 
tween the  light  of  the  sun  and  polar  light,  see  Sir  John  Herschel's  Re- 
mit* of  Aitron.  Observ.  at  the  Cape  of  Good  Hope,  1847,  p.  351.  Arago, 
in  the  Comptes  Rendus  pour  1838,  t.  vii.,  p.  956,  has  referred  to  the  in- 
genious application  of  Breguet's  improved  Wheatstone's  rotatory  ap- 
paratus for  determining  between  the  theories  of  emission  and  undula- 
tion, since,  according  to  the  former,  light  moves  more  rapidly  through 
water  than  through  air,  while,  according  to  the  latter,  it  moves  more 
rapidly  through  air  than  through  water.  (Compare  also  Comptes  Ren- 
dus pour  1850,  t.  xxx.,  p.  489-495,  556.) 


VELOCITY    OF    ELECTRICITY.  87 

be  satisfactorily  compared  with  the  results  deduced  from  ob- 
servations on  aberration  and  on  the  satellites. 

The  attention  of  physicists  has  been  powerfully  attracted 
to  the  experiments  on  the  velocity  of  the  transmission  of 
electricity,  recently  conducted  in  the  United  States  by  Walk- 
er during  the  course  of  his  electro-telegraphic  determina- 
tions of  the  terrestrial  longitudes  of  Washington,  Philadel- 
phia, New  York,  and  Cambridge.  According  to  Steinheil's 
description  of  these  experiments,  the  astronomical  clock  of 
the  Observatory  at  Philadelphia  was  brought  to  correspond 
so  perfectly  with  Morse's  writing  apparatus  on  the  tele- 
graphic line,  that  this  clock  marked  its  own  course  by  points 
on  the  endless  paper  fillets  of  the  apparatus.  The  electric 
telegraph  instantaneously  conveys  each  of  these  clock  times 
to  the  other  stations,  indicating  to  these  the  Philadelphia 
time  by  a  succession  of  similar  points  on  the  advancing  pa- 
per fillets.  In  this  manner,  arbitrary  signs,  or  the  instant 
of  a  star's  transit,  may  be  similarly  noted  down  at  the  sta- 
tion by  a  mere  movement  of  the  observer's  finger  on  the  stop. 
"The  special  advantage  of  the  American  method  consists," 
as  Steinheil  observes,  "  in  its  rendering  the  determination  of 
time  independent  of  the  combination  of  the  two  senses,  sight 
and  hearing,  as  the  clock  notes  its  own  course,  and  indicates 
the  instant  of  a  star's  transit  (with  a  mean  error,  according 
to  Walker's  assertion,  of  only  the  70th  part  of  a  second).  A 
constant  difference  between  the  compared  clock  times  at 
Philadelphia  and  at  Cambridge  is  dependent  upon  the  time 
occupied  by  the  electric  current  in  twice  traversing  the 
closed  circle  between  the  two  stations." 

Eighteen  equations  of  condition,  from  measurements  made 
on  conducting  wires  of  1050  miles,  gave  for  the  velocity  of 
transmission  of  the  hydro-galvanic  current  18,700  miles,* 
which  is  fifteen  times  less  than  that  of  the  electric  current 
in  Wheatstone's  rotatory  disks.  As  in  Walker's  remarkable 
experiments  two  zvires  were  not  used,  but  half  of  the  con- 

*  Steinheil,  in  Schumacher's  Astr.  Naekr.,  No.  679  (1849),  s.  97-100; 
Walker,  in  the  Proceedings  of  the  American  Philosophical  Society,  vol. 
v.,  p.  128.  (Compare  earlier  propositions  of  Pouillet  in  the  Comptes 
Rendus,  t.  xix.,  p.  1386.)  The  more  recent  ingenious  experiments  of 
Mitchel,  Director  of  the  Observatory  at  Cincinnati  (Gould's  Astron. 
Journal,  Dec.,  1849,  p.  3,  On  the  Velocity  of  the  Electric  Wave'),  and  the 
investigations  of  Fizeau  and  Gounelle  at  Paris,  in  April,  1850,  differ 
both  from  Wheatstone's  and  Walker's  results.  The  experiments  re- 
corded in  the  Comptes  Rendut,  t.  xxx.,  p.  439,  exhibit  striking  differ 
ences  between  iron  and  copper  as  conducting  media. 


88  COSMOS. 

duction,  to  use  a  conventional  mode  of  expression,  passed 
through  the  moist  earth,  we  should  seem  to  be  justified  in 
concluding  that  the  velocity  of  the  transmission  of  electricity 
depends  upon  the  nature  as  well  as  the  dimensions*  of  the 
medium.  Bad  conductors  in  the  voltaic  circuit  become  more 
powerfully  heated  than  good  conductors ;  and  the  experi- 
ments lately  made  by  Eiessf  show  that  electric  discharges 
are  phenomena  of  a  very  various  and  complicated  nature. 
The  views  prevailing  at  the  present  day  regarding  what  is 
usually  termed  "  connection  through  the  earth"  are  opposed 
to  the  hypothesis  of  linear,  molecular  conduction  between 
the  extremities  of  the  wires,  and  to  the  conjectures  of  the 
impediments  to  conduction,  of  accumulation,  and  disruption 
in  a  current,  since  what  was  formerly  regarded  as  interme- 
diate conduction  in  the  earth  is  now  conjectured  to  belong 
exclusively  to  an  equalization  or  restoration  of  the  electric 
tension. 

Although  it  appears  probable,  from  the  extent  of  accura- 
cy at  present  attainable  in  this  kind  of  observation,  that  the 
constant  of  aberration,  and,  consequently,  the  velocity  of 
light,  is  the  same  for  all  fixed  stars,  the  question  has  fre- 
quently been  mooted  whether  it  be  not  possible  that  there 
are  luminous  cosmical  bodies  whose  light  does  not  reach  us, 
in  consequence  of  the  particles  of  air  being  turned  back  by 
the  force  of  gravitation  exercised  by  the  enormous  masses 
of  these  bodies.  The  theory  of  emission  gives  a  scientific 
form  to  these  imaginative  speculations.^  I  here  only  refer 

*  See  PoggendorflPs  Annalen,  bd.  Ixxiii.,  1848,  s.  337,  and  Pouillet, 
Comptes  Rendus,  t.  xxx.,  p.  501. 

t  Riess,  in  PoggendorfTs  Ann.,  bd.  78,  s.  433.  On  the  non-conduc 
tion  of  the  intermediate  earth,  see  the  important  experiments  of  Guille- 
miu,  Sur  le  courant  dans  une  pile  isolte  ct  sans  communication  entre  let 
pdles  in  the  Comptes  Rendus,  t.  xxix.,  p.  521.  "  Quand  on  remplace 
un  fil  par  la  terre,  dans  les  telegraphes  electriques,  la  terre  sort  plut6t 
de  reservoir  commun,  quo  de  moyen  d'union  entre  les  deux  extremi- 
tes  du  fil."  "  When  the  earth  is  substituted  for  half  the  circuit  in  the 
electric  telegraph,  it  serves  rather  as  a  common  reservoir  than  as  a 
means  of  connection  between  the  two  extremities  of  the  wire." 

t  Madler,  Astr.,  a.  380;  also  Laplace,  according  to  Moigno,  Repertoire 
d'Optique  Moderne,  1847,  t.  i.,  p.  72 :  "  Selon  la  theorie  de  l'6mission 
on  croit  pouvoir  demontrer  que  si  le  diametre  d'une  6toile  fixe  serait  250 
fois  plus  grand  que  celui  du  soleil,  sa  densite  restant  la  meme,  1'attrac- 
tion  exercee  a  sa  surface  detruirait  la  quantite  de  mouvement,  de  la 
moldcule  lumineuse  Praise,  de  sorte  qu'elle  serait  invisible  a  de  gramles 
distances."  "  It  seems  demonstrable  by  the  theory  of  emission  that  if 
the  diameter  of  a  fixed  star  be  250  times  greater  than  that  of  the  sun — 
its  density  remaining  the  same — the  attraction  exercised  on  the  surface 


STELLAR  LIGHT.  89 

to  such  views  because  it  will  be  necessary  in  the  sequel  that 
we  should  consider  certain  peculiarities  ef  motion  ascribed 
to  Procyon,  which  appeared  to  indicate  a  disturbance  from 
dark  cosmical  bodies.  It  is  the  object  of  the  present  portion 
of  this  work  to  notice  the  different  directions  to  which  scien- 
tific inquiry  had  inclined  at  the  period  of  its  composition  and 
publication,  and  thus  to  indicate  the  individual  character 
of  an  epoch  in  the  sidereal  as  well  as  the  telluric  sphere. 

The  photometric  relations  (relations  of  brightness)  of  the 
self-luminous  bodies  with  which  the  regions  of  space  are 
filled,  have  for  more  than  two  thousand  years  been  an  ob- 
ject of  scientific  observation  and  inquiry.  The  description 
of  the  starry  firmament  did  not  only  embrace  determinations 
of  places,  the  relative  distances  of  luminous  cosmical  bodies 
from  one  another  and  from  the  circles  depending  on  the  ap- 
parent course  of  the  sun  and  on  the  diurnal  movement  of 
the  vault  of  heaven,  but  it  also  considered  the  relative  in- 
tensity of  the  light  of  the  stars.  The  earliest  attention  of 
mankind  was  undoubtedly  directed  to  this  latter  point,  in- 
dividual stars  having  received  names  before  they  were  ar- 
ranged Avith  others  into  groups  and  constellations.  Among 
the  wild  tribes  inhabiting  the  densely- wooded  regions  of  the 
Upper  Orinoco  and  the  Atabapo,  where,  from  the  impene- 
trable nature  of  the  vegetation,  I  could  only  observe  high 
culminating  stars  for  determinations  of  latitude,  I  frequently 
found  that  certain  individuals,  more  especially  old  men,  had 
designations  for  Canopus,  Achernar,  the  feet  of  the  Centaur, 
and  a  in  the  Southern  Cross.  If  the  catalogue  of  the  con- 
stellations known  as  the  Catasterisjns  of  Eratosthenes  can 
lay  claim  to  the  great  antiquity  so  long  ascribed  to  it  (between 
Autolycus  of  Pitane  and  Timocharis,  and  therefore  nearly  a 

would  destroy  the  amount  of  motion  emitted  from  the  luminous  mole- 
cule, so  that  it  would  be  invisible  at  great  distances."  If,  with  Sir 
William  Herschel,  we  ascribe  to  Arcturus  an  apparent  diameter  of  0"-1, 
it  follows  that  the  true  diameter  of  this  star  is  only  eleven  times  greater 
than  that  of  our  sun.  (Cosmos,  vol.  i.,  p.  148.)  From  the  above  con- 
siderations on  one  of  the  causes  of  non-luminosity,  the  velocity  of  light 
must  be  very  different  in  cosmical  bodies  of  different  dimensions.  This 
has,  however,  by  no  means  been  confirmed  by  the  observations  hitherto 
made.  Arago  says  in  the  Comptes  Rendus,  t.  viii.,  p.  326,  "  Les  expe- 
riences sur  1'egale  deviation  prismatique  des  etoiles,  vers  lesquelles  la 
terre  marche  ou  dont  elle  s'eloigne,  rend  compte  de  I'6galit6  de  vitesse 
apparente  de  toutes  les  etoiles."  "Experiments  made  on  the  equal 
prismatic  deviation  of  the  stars  toward  which  the  earth  is  moving,  and 
from  which  it  is  receding,  explain  the  apparent  equality  of  velocity  in 
the  ray«  of  all  the  stars." 


90  COSMOS. 

century  and  a  half  before  the  time  of  Hipparchus),  we  pos- 
sess in  the  astronomy  of  the  Greeks  a  limit  for  the  period 
when  the  fixed  stars  had  not  yet  been  arranged  according 
to  their  relative  magnitudes.  In  the  enumeration  of  the 
stars  belonging  to  each  constellation,  as  given  in  the  Catas- 
terisms,  frequent  reference  is  made  to  the  number  of  the 
largest  and  most  luminous,  or  of  the  dark  and  less  easily  rec- 
ognized stars  ;*  but  we  find  no  relative  comparison  of  the 
stars  contained  in  the  different  constellations.  The  Catas- 
terisms  are,  according  to  Bernhardy,  Baehr,  and  Letronne, 
more  than  two  hundred  years  less  ancient  than  the  catalogue 
of  Hipparchus,  and  are,  besides,  a  careless  compilation  and 
a  mere  extract  from  the  Poeticum  Astronomicum  (ascribed 
to  Julius  Hyginus),  if  not  from  the  poem  'Epju^f  of  the  older 
Eratosthenes.  The  catalogue  of  Hipparchus,  which  we  pos- 
sess in  the  form  given  to  it  in  the  Almagest,  contains  the  ear- 
liest and  most  important  determination  of  classes  of  magni- 
tude (gradations  of  brightness)  of  1022  stars,  and  therefore 
of  about  one  fifth  of  all  the  stars  in  the  firmament  visible  to 
the  naked  eye,  and  ranging  from  the  first  to  the  sixth  mag- 
nitude inclusive.  It  remains  undetermined  whether  these 
estimates  are  all  due  to  Hipparchus,  or  whether  they  do  not 
rather  appertain  in  part  to  the  observations  of  Timocharis 
or  Aristyllus,  which  Hipparchus  frequently  used. 

This  work  constituted  the  important  basis  on  which  was 
established  the  science  of  the  Arabs  and  of  the  astronomers 
of  the  Middle  Ages  :  the  practice,  transmitted  to  the  nine- 
teenth century,  of  limiting  the  number  of  stars  of  the  first 
magnitude  to  15  (although  Madler  counts  18,  and  Riimker, 
after  a  more  careful  observation  of  the  southern  celestial  hem- 
isphere, upward  of  20),  takes  its  origin  from  the  classifica- 
tion of  the  Almagest,  as  given  at  the  close  of  the  table  of 
stars  in  the  eighth  book.  Ptolemy,  referring  to  natural  vi- 
sion, called  all  stars  dark  which  were  fainter  than  those  of 
his  sixth  class ;  and  of  this  class  he  singularly  enough  only 
instances  49  stars  distributed  almost  equally  over  both  hem- 
ispheres. Considering  that  the  catalogue  enumerates  about 
one  fifth  of  all  the  fixed  stars  visible  to  the  naked  eye,  it 
should,  according  to  Argelander's  investigations,  have  given 

*  Eratosthenes,  Catasterismi,  ed.  Schaubach,  1795,  and  Eratotthenica, 
ed.  G.  Bernhardy,  1822,  p.  110-116.  A  distinction  is  made  between 
stars  hafinpovc  (jieyuTiOvf)  and  afjtavpovf  (cap.  2,  11,  41).  Ptolemy  also 
limits  ol  {ipopfyuToi  to  those  stars  which  do  not  regularly  belong  to  a  con- 
stellation. 


MAGNITUDES  OF  STARS.  91 

640  stars  of  .the  sixth  magnitude.  The  nebulous  stars  (ve- 
deXoeLdds')  of  Ptolemy  and  of  the  Pseudo-Eratosthenian  Ca- 
iasterisms  are  mostly  small  stellar  swarms,*  appearing  like 
nebulae  in  the  clearer  atmosphere  of  the  southern  hemisphere. 
I  more  particularly  base  this  conjecture  on  the  mention  of  a 
nebula  in  the  right  hand  of  Perseus.  Galileo,  who,  like  the 
Greek  and  Arabian  astronomers,  was  unacquainted  with  the 
nebula  in  Andromeda  which  is  visible  to  the  naked  eye,  says 
in  his  Nuntius  sidereus  that  stellce  nebulosts  are  nothing 
more  than  stellar  masses  scattered  in  shining  groups  through 
the  ether  (areolce,  sparsim  per  cethera  fulgent).^  The  ex- 
pression (r&v  fj,eydA.d)v  raft^),  the  order  of  magnitudes,  al- 
though referring  only  to  luster,  led,  as  early  as  the  ninth  cen- 
tury, to  hypotheses  on  the  diameters  of  stars  of  different  bright- 
ness ;J  as  if  the  intensity  of  light  did  not  depend  on  the  dis- 
tance, volume,  and  mass,  as  also  on  the  peculiar  character 
of  the  surface  of  a  cosmical  body  in  more  or  less  favoring  the 
process  of  light. 

At  the  period  of  the  Mongolian  supremacy,  when,  in  the 
fifteenth  century,  astronomy  nourished  at  Samarcand,  under 
Timur  Ulugh  Beg,  photometric  determinations  were  facili- 
tated by  the  subdivision  of  each  of  the  six  classes  of  Hippar- 
chus  and  Ptolemy  into  three  subordinate  groups ;  distinctions, 
for  example,  being  drawn  between  the  small,  intermediate, 
and  large  stars  of  the  second  magnitude — an  attempt  which 
reminds  us  of  the  decimal  gradations  of  Struve  and  Argelan- 
der.§  This  advance  in  photometry,  by  a  more  exact  determ- 
ination of  degrees  of  intensity,  is  ascribed  in  Ulugh  Beg's 
tables  to  Abdurrahman  Sufi,  who  wrote  a  work  "  on  the 
knowledge  of  the  fixed  stars,"  and  was  the  first  who  men- 
tions one  of  the  Magellanic  clouds  under  the  name  of  the 
White  Ox.  Since  the  discovery  and  gradual  improvement 
of  telescopic  vision,  these  estimates  of  the  gradations  of  light 
have  been  extended  far  below  the  sixth  class.  The  desire 
of  comparing  the  increase  and  decrease  of  light  in  the  newly- 

*  Plot.  Almas.,  ed  Halma,  torn,  ii.,  p.  40,  and  in  Eratosth.  Catast., 
cap.  22,  p.  18:  rj  de  KtQa/.Tj  Kai  ij  apnr)  uvaifTOf  dparai,  6ia  de  ve0e?.u<5ot»f 
avarpo<j>jjc  do/ccl  TLGIV  opuadai.  Thus,  too,  Geminus,  Pheen.  (ed.  Hilder, 
1590),  p.  46.  t  Cosmos,  vol.  ii.,  p.  330,  331. 

t  Muhamedis  Alfragani  Chronologica  et  Ast.  Elementa,  1590,  cap. 
xxiv.,  p.  118. 

$  Some  MSS.  of  the  Almagest  refer  to  such  subdivisions  or  interme- 
diate classes,  as  they  add  the  words  pei&v  or  ehdaauv  to  the  determ- 
ination of  magnitudes.  (Cod.  Paris,  No.  2389.)  Tycho  expressed  thia 
increase  or  diminution  by  points. 


92  COSMOS. 

appeared  stars  in  Cygnus  and  Ophiuchus  (tie  former  of  which 
continued  luminous  for  twenty-one  years),  with  the  bright- 
ness of  other  stars,  called  attention  to  photometric  determina- 
tions. The  so-called  dark  stars  of  Ptolemy,  which  were  he- 
low  the  sixth  magnitude,  received  numerical  designations 
according  to  the  relative  intensity  of  their  light.  "  Magni- 
tudes, from  the  eighth  down  to  the  sixteenth,"  says  Sir  John 
Herschel,  "  are  familiar  to  those  who  are  in  the  practice  of 
using  powerful  instruments.*  But  at  this  faint  degree  of 
brightness,  the  denominations  for  the  different  gradations  in 
the  scale  of  magnitudes  are  very  undetermined,  for  Struve 
occasionally  classes  among  the  twelfth  or  thirteenth  stars 
which  Sir  John  Herschel  designates  as  belonging  to  the 
eighteenth  or  twentieth  magnitudes. 

The  present  is  not  a  fitting  place  to  discuss  the  merits  of 
the  very  different  methods  which  have  been  adopted  for  the 
measurement  of  light  within  the  last  hundred  and  fifty  years, 
from  Auzout  and  Huygens  to  Bouguer  and  Lambert ;  and 
from  Sir  William  Herschel,  K-umford,  and  Wollaston,  to  Stein- 
heil  and  Sir  John  Herschel.  It  will  be  sufficient  for  the  ob- 
ject of  this  work  briefly  to  indicate  the  different  methods. 
These  were  a  comparison  of  the  shadows  of  artificial  lights, 
differing  in  numbers  and  distance ;  diaphragms ;  plane-glass- 
es of  different  thickness  and  color  ;  artificial  stars  formed  by 
reflection  on  glass  spheres  ;  the  juxtaposition  of  two  seven- 
feet  telescopes,  separated  by  a  distance  which  the  observer 
could  pass  in  about  a  second ;  reflecting  instruments  in  which 
two  stars  can  be  simultaneously  seen  and  compared,  when 
the  telescope  has  been  so  adjusted  that  the  star  directly  ob- 
served gives  two  images  of  like  intensity  ;t  an  apparatus  hav» 

*  Sir  John  Herschel,  Outlines  of  Astr.,  p.  520-27. 

t  This  is  the  application  of  reflecting  sextants  to  the  determination 
of  the  intensity  of  stellar  light ;  of  this  instrument  I  made  greater  use 
when  in  the  tropics  than  of  the  diaphragms  recommended  to  me  by 
Borda.  I  began  my  investigation  under  the  clear  skies  of  Cumana,  and 
continued  them  subsequently  till  1803,  but  under  less  favorable  condi- 
tions, on  the  elevated  plateaux  of  the  Andes,  and  on  the  coasts  of  the 
Pacific,  near  Guayaquil.  I  had  formed  an  arbitrary  scale,  in  which  I 
marked  Sirius,  as  the  brightest  of  all  the  fixed  stars,  equal  to  100;  the 
stars  of  the  first  magnitude  between  100  and  80,  those  of  the  second 
magnitude  between  80  and  60,  of  the  third  between  60  and  45,  of  the 
fourth  between  45  and  30,  and  those  of  the  fifth  between  30  and  20.  I 
especially  measured  the  constellations  of  Argo  and  Grus,  in  which  I 
thought  I  had  observed  alterations  since  the  time  of  Lacaille.  It  seemed 
to  me,  after  a  careful  combination  of  magnitudes,  using  other  stars  as 
intermediate  gradations,  that  Sirius  was  as  much  brighter  than  Canopus, 
as  a  Centauri  than  Achernar.  My  numbers  can  not,  on  accoupt  of  tho 


PHOTOMETRIC  METHODS.  93 

ing  (iii  front  of  the  object-glass)  a  mirror  and  diaphragms, 
whose  rotation  is  measured  on  a  ring ;  telescopes  with  di- 
vided object-glasses,  on  either  half  of  which  the  stellar  light 
is  received  through  a  prism ;  astrometers*  in  which  a  prism 
reflects  the  image  of  the  moon  or  of  Jupiter,  and  concentrates 
it  through  a  lens  at  different  distances  into  a  star  more  or 
less  bright.  Sir  John  Herschel,  who  has  been  more  zealous- 
ly engaged  than  any  other  astronomer  of  modern  times  in 
making  numerical  determinations  in  both  hemispheres  of  the 
intensity  of  light,  confesses  that  the  practical  application  of 
exact  photometric  methods  must  still  be  regarded  as  a  "  de- 
above-mentioned  mode  of  classification,  be  compared  directly  with 
those  which  Sir  John  Herschel  made  public  as  early  as  1838.  (See  my 
Recneil  d'Observ.  Astr.,  vol.  i.,  p.  Ixxi.,  and  Rclat.  Hist,  du  Voyage  aux 
Regions  Equin.,  t.  i.,  p.  518  and  624;  also  Lettre  de  M.  de  Humboldt  a 
M.  Schumacher  en  Fevr.,  1839,  in  the  Astr.  Nachr.,  No.  374.)  In  this 
letter  I  wrote  as  follows :  "  M.  Arago,  qui  possede  des  moyens  photo- 
metriques  entierement  difierents  de  ceux  qui  ont  ete  publics  jusqu'ici, 
m'avait  rassure  sur  la  partie  des  erreurs  qui  pouvaient  provenir  du  change- 
ment  d'inclinaison  d'un  miroir  entame  sur  la  face  interieure.  H  blame 
d'ailleurs  le  principe  de  ma  methode  et  le  regarde  comme  peu  suscep- 
tible de  perfectionnement,  non  seulement  a  cause  de  la  difference  des 
angles  entre  1'etoile  vue  directement  et  celle  qui  est  amenee  par  reflex- 
ion, mais  surtout  parceque  le  resultat  de  la  mesure  d'intensite  dfepend 
de  la  partie  de  1'ceil  qui  se  trouve  en  face  de  1'oculaire.  II  y  a  erreur 
lorsque  la  pupille  n'est  pas  tres  exactement  a  la  hauteur  de  la  limite  in- 
ferieure  de  la  portion  non  eutamee  du  petit  miroir."  "  M.  Arago,  who 
possesses  photometric  data  differing  entirely  from  those  hitherto  pub- 
lished, had  instructed  me  in  reference  to  those  errors  which  might  arise 
from  a  change  of  inclination  of  a  mirror  silvered  on  its  inner  surface. 
He  moreover  blames  the  principle  of  my  method,  and  regards  it  as  lit- 
tle susceptible  of  correctness,  not  only  on  account  of  the  difference  of 
angles  between  the  star  seen  directly  and  by  reflection,  but  especially 
because  the  result  of  the  amount  of  intensity  depends  on  the  part  of  the 
eye  opposite  to  the  ocular  glass.  There  will  be  an  error  in  the  observ- 
ations when  the  pupil  is  not  exactly  adjusted  to  the  elevation  of  the 
lower  limit  of  the  unplated  part  of  the  small  mirror." 

*  Compare  Steinheil,  Elemente  der  Helligkeils-Messungen  am  Sternen- 
himmel  Munchen,  1836  (Schum.,  Astr.  Nachr.,  No.  609),  and  John  Her- 
schel, Results  of  Astronomical  Observations  made  during  the  Years  1834 
-1838  at  the  Cape  of  Good  Hope  (Lond.,  1847),  p.  353-357.  Seidel  at- 
tempted in  1846  to  determine  by  means  of  Steinheil's  photometer  the 
quantities  of  light  of  several  stars  of  the  first  magnitude,  which  attain 
the  requisite  degree  of  latitude  in  our  northern  latitudes.  Assuming 
Vega  to  be  =1,  he  finds  for  Sirius  5-13 ;  for  Rigel,  whose  luster  appears 
to  be  on  the  increase,  1-30;  for  Arcturus,  0-84;  for  Capella,  0-83;  for 
Procyon,  071;  for  Spica,  0-49;  for  Atair,  0-40;  for  Aldebaran,  0-36; 
for  Deneb,  0-35;  for  Regulns,  0-34;  for  Pollux,  0-30;  he  does  not  give 
the  intensity  of  the  light  of  Betelgeux,  on  account  of  its  being  a  varia- 
ble star,  as  was  particularly  manifested  between  1836  and  1839.  (Ont 
tiite*,  p.  523  ) 


94  COSMOS. 

eideratum  in  astronomy,"  and  that  "  photometry  is  yec  /*.  *« 
infancy."  The  increasing  interest  taken  in  variable  swrs, 
and  the  recent  celestial  phenomenon  of  the  extraordinary  in- 
crease of  light  exhibited  in  the  year  1837  in  a  star  of  the  con- 
stellation Argo,  has  made  astronomers  more  sensible  of  the 
importance  of  obtaining  certain  determinations  of  light. 

It  is  essential  to  distinguish  between  the  mere  arrangement 
of  stars  according  to  their  luster,  without  numerical  estimates 
of  the  intensity  of  light  (an  arrangement  adopted  by  Sir  John 
Herschel  in  his  Manual  of  Scientific  Inquiry  prepared  for 
the  Use  of  the  Navy),  and  classifications  in  which  intensity 
of  light  is  expressed  by  numbers,  under  the  form  of  so-called 
relations  of  magnitude,  or  by  more  hazardous  estimates  of  the 
quantities  of  radiated  light.*  The  first  numerical  scale,  based 
on  estimates  calculated  with  the  naked  eye,  but  improved  by 
an  ingenious  elaboration  of  the  materials!  probably  deserves 
the  preference  over  any  other  approximative  method  practi- 
cable in  the  present  imperfect  condition  of  photometrical  in- 
struments, however  much  the  exactness  of  the  estimates  must 
be  endangered  by  the  varying  powers  of  individual  observers 
— the  serenity  of  the  atmosphere — the  different  altitudes  of 
widely-distant  stars,  which  can  only  be  compared  by  means 
of  numerous  intermediate  stellar  bodies — and  above  all  by  the 
unequal  color  of  the  light.  Very  brilliant  stars  of  the  first 
magnitude,  such  as  Sirius  and  Canopus,  a  Centauri  and  Acher- 
nar,  Deneb  and  Vega,  on  account  of  their  white  light,  admit 
far  less  readily  of  comparison  by  the  naked  eye  than  fainter 
stars  below  the  sixth  and  seventh  magnitudes.  Such  a  com- 
parison is  even  more  difficult  when  we  attempt  to  contrast 
yellow  stars  of  intense  light,  like  Procyon,  Capella,  or  Atair, 
with  red  ones,  like  Aldebaran,  Arcturus,  and  Betelgeux.J 

*  Compare,  for  the  numerical  data  of  the  photometric  results,  four 
tables  of  Sir  John  Herschel's  Astr.  Obs.  at  the  Cape,  a),  p.  341 ;  b),  p. 
367-371 ;  c),  p.  440  ;  and  d),  in  his  Outlines  of  Astr.,  p.  522-525,  645- 
646.  For  a  mere  arrangement  without  numbers,  see  the  Manual  of 
Scientific  Inquiry  prepared  for  the  Use  of  the  Navy,  1819,  p.  12.  In 
order  to  improve  the  old  conventional  mode  of  classing  the  stars  accord- 
ing to  magnitudes,  a  scale  of  photometric  magnitudes,  consisting  in  the 
addition  of  0-41,  as  explained  more  in  detail  in  Astr.  Obs.  at  the  Cape,  p. 
370.  has  been  added  to  the  vulgar  scale  of  magnitudes  in  the  Outlines  of 
Astronomy,  p.  645,  and  these  scales  are  subjoined  to  this  portion  of  the 
present  work,  together  with  a  list  of  northern  and  southern  stars. 

t  Argelander,  Durchmusterung  des  nordl.  Himmels  zwischen  45°  und 
80°  Decl.  1846,  s.  xxiv.-xxvi. ;  Sir  John  Herschel,  Astr.  Obscrv.  al  the 
Cape  of  Good  Hope,  p.  327,  340,  365. 

t  Op.  cit.,  p.  304,  aud  Outl.,  p.  522. 


PHOTOMETRY.  95 

Sir  John  Herschcl  has  endeavored  to  determine  the  rela- 
tion between  the  intensity  of  solar  light  and  that  of  a  star  of 
the  first  magnitude  by  a  photometric  comparison  of  the  moor, 
with  the  double  star  a  Centauri  of  the  southern  hemisphere, 
which  is  the  third  in  brightness  of  all  the  stars.  He  thus 
fulfilled  (as  had  been  already  done  by  "Wollaston)  a  wish  ex- 
pressed by  John  Michell*  as  early  as  1767.  Sir  John  Her- 
schel  found  from  the  mean  of  eleven  measurements  conduct- 
ed with  a  prismatic  apparatus,  that  the  full  moon  was  27,408 
times  brighter  than  a  Centauri.  According  to  Wollaston,  the 
light  of  the  sun  is  801,072  times  brighter  than  the  full  moon  ;f 
whence  it  follows  that  the  light  transmitted  to  us  from  the 
sun  is  to  the  light  which  we  receive  from  a  Centauri  as 
22,000  millions  to  1.  It  seems,  therefore,  very  probable, 
when,  in  accordance  with  its  parallax,  we  take  into  account 
the  distance  of  the  star,  that  its  (absolute)  proper  luminosity 
exceeds  that  of  our  sun  by  2f-  times.  Wollaston  found  the 
brightness  of  Sirius  20,000  million  times  fainter  than  that  of 
the  sun.  From  what  we  at  present  believe  to  be  the  paral- 
lax of  Sirius  (0-"230),  its  actual  (absolute)  intensity  of  light 
exceeds  that  of  the  sun  63  times4  Our  sun  therefore  be- 
longs, in  reference  to  the  intensity  of  its  process  of  light,  to 
the  fainter  fixed  stars.  Sir  John  Herschel  estimates  the  in- 
tensity of  the  light  of  Sirius  to  be  equal  to  the  light  of  nearly 

*  Philos.  Transact.,  vol.  Ivii.,  for  the  year  1767,  p.  234. 

t  Wollaston,  in  the  Philos.  Transact,  for  1829,  p.  27.  Herschel'a 
Outlines,  p.  553.  Wollaston's  comparison  of  the  light  of  the  sun  with 
that  of  the  moon  was  made  in  1799,  and  was  based  on  observations  of 
the  shadows  thrown  by  lighted  wax  tapers,  while  in  the  experiments 
made  on  Sirius  in  1826  and  1827,  images  reflected  from  thermometer 
bulbs  were  employed.  The  earlier  data  of  the  intensity  of  the  sun'a 
light,  compared  with  that  of  the  moon,  differ  widely  from  the  results 
here  given.  They  were  deduced  by  Michelo  and  Euler,  from  theoret- 
ical grounds,  at  450,000  and  374,000,  and  by  Bouguer,  from  measure- 
ments of  the  shadows  of  the  light  of  wax  tapers,  at  only  300,000.  Lam- 
bert assumes  Venus,  in  her  greatest  intensity  of  light,  to  be  3000  times 
fainter  than  the  full  moon.  According  to  Steinheil,  the  sun  must  be 
3,286,500  times  further  removed  from  the  earth  than  it  is,  in  order  to 
appear  like  Arcturus  to  the  inhabitants  of  our  planet  (Struve,  Stellarum 
Compositarnm  Mcnsuree  Micrometricee,  p.  clxiii.);  and,  according  to 
Sir  John  Herschel,  the  light  of  Arcturus  exhibits  only  half  the  intensity 
of  3anopus. — Herschel,  Observ.  at  the  Cape,  p.  34.  All  these  conditions 
of  intensity,  more  especially  the  important  comparison  of  tho  bright 
ness  of  the  sun,  the  full  moon,  and  of  the  ash-colored  light  of  our  satel- 
lite, which  varies  so  greatly  according  to  the  different  positions  of  the 
earth  considered  as  a  reflecting  body,  deserve  further  and  serious  in- 
vestigation. 

\  Quit.  <>f  Astr.,  p.  553  ;  Aslr.  Observ.  at  the  Cape,  p.  363. 


96  COSMOS. 

two  hundred  stars  of  the  sixth  magnitude.  Since  it  is  very 
probable,  from  analogy  with  the  experiments  already  made, 
that  all  cosmical  bodies  are  subject  to  variations  both  in  their 
movements  through  space  and  in  the  intensity  of  their  light, 
although  such  variations  may  occur  at  very  long  and  unde- 
termined periods,  it  is  obvious,  considering  the  dependence 
of  all  organic  life  on  the  sun's  temperature  and  on  the  intens- 
ity of  its  light,  that  the  perfection  of  photometry  constitutes 
a  great  and  important  subject  for  scientific  inquiry.  Such 
an  improved  condition  of  our  knowledge  can  render  it  alone 
possible  to  transmit  to  future  generations  numerical  determ- 
inations of  the  photometric  condition  of  the  firmament.  By 
these  means  we  shall  be  enabled  to  explain  numerous  geog- 
nostic  phenomena  relating  to  the  thermal  history  of  our  at- 
mosphere, and  to  the  earlier  distribution  of  plants  and  ani- 
mals. Such  considerations  did  not  escape  the  inquiring  mind 
of  William  Herschel,  who,  more  than  half  a  century  ago,  be- 
fore the  close  connection  between  electricity  and  magnetism 
had  been  discovered,  compared  the  ever-luminous  cloud-en- 
velopes of  the  sun's  body  with  the  polar  light  of  our  own  ter- 
restrial planet.* 

Arago  has  ascertained  that  the  most  certain  method  for 
the  direct  measurement  of  the  intensity  of  light  consists  in 
observing  the  complementary  condition  of  the  colored  rings 
seen  by  transmission  and  reflection.  I  subjoin  in  a  note,t  in 

*  William  Herschel,  On  the  Nature  of  the  Sun  and  Fixed  Stars,  in 
the  Philos.  Transact,  for  1795,  p.  62  ;  and  On  the  Changes  that  happen 
to  the  Fixed  Stars,  in  the  Philos.  Transact,  for  1796,  p.  186.  Gomparo 
also  Sir  John  Herschel,  Obsero.  at  the  Cape,  p.  350-352. 

t  Extract  of  a  Letter  from  M.  Arago  to  M.  de  Humboldt,  May,  1850. 

(a.)  Mesurcs  Photom6triqucs. 

"  II  n'existe  pas  de  photometre  proprement  dit,  c'est-a-dire  d'instru- 
ment  donuant  1'intensite  d'une  lumiere  isol^e ;  le  photometre  de  Les- 
lie, a  1'aide  duquel  il  avail  eu  1'audace  de  vouloir  comparer  la  lumiere 
de  la  lune  a  la  lumiere  du  soleil,  par  des  actions  calonfiques,  est  com- 
pletement  defectueux.  .T'ai  prouve,  en  effet,  que  ce  preteudu  photo- 
metre  monte  quand  on  1'expose  a  la  lumiere  du  soleil,  qu'il  descend 
sous  1'action  de  la  lumiere  du  feu  ordinaire,  et  qu'il  reste  complete- 
ment  stationnaire  lorsqu'il  re9oit  la  lumiere  d'une  lampe  d'Argand'. 
Tout  ce  qu'on  a  pu  faire  jusqu'ici,  c'est  de  comparer  entr'elles  deux  lu- 
mieres  en  presence,  et  cette  comparaison  n'est  meme  a  1'abri  de  toute 
objection  que  lorsqu'on  ramene  ces  deux  lumieres  a  I'egalit^  par  un 
amublissement  graduel  de  la  lumiere  la  plus  forte.  C'est  comme  crite- 
rium  de  cette  egalit6  que  j'ai  employ^  les  anneaux  colores.  Si  on  place 
I'une  sur  1'autre  deux  lentilles  d'un  long  foyer,  il  se  forme  autour  de 
leur  point  de  contact  des  anneaux  colored  tant  par  voie  de  reflexion  que 
par  voi  5  de  transmission.  Les  anueaux  reflechia  sout  conipleineutaires 


PHOTOMETRY.  97 

his  own  words,  the  results  of  my  friend's  photometric  method, 
to  which  he  has  added  an  account  of  the  optical  principle 
oa  which  his  cyanometer  is  based. 

en  couleur  des  anneaux  transmis;  ces  deux  series  d'anneaux  se  neu- 
tralisent  mutuellement  qoand  les  deux  lumieres  qui  les  Ibrment  et  qui 
arrivent  simultanement  sur  les  deux  lentilles,  sont  egales  entr'elles. 

"  Dans  le  cas  contraire  on  voit  des  traces  ou  d'anneaux  reflechis  ou 
d'anneaux  transrais,  suivant  quo  la  lumiere  qui  forme  les  premiers,  est 
plus  forte  ou  plus  foible  que  la  lumiere  a  laquelle  on  doit  les  seconds. 
C'est  dans  ce  sens  settlement  que  les  anneaux  colores  jouent  un  role 
dans  les  mesures  de  la  lumiere  auxquelles  je  me  suis  livre." 

(6.)  Cyanometre. 

"  Mon  cyanometre  est  une  extension  de  mon  polariscope.  Ce  der- 
nier instrument,  comma  tu  sais,  se  compose  d'un  tube  ferme  £  1'une  de 
ses  extremites  par  une  plaque  de  cristal  de  roche  perpendiculaire  a 
I'axe,  de  5  millimetres  d'epaisseur ;  et  d'un  prisme  doue  de  la  double 
refraction,  place  du  cote  de  1'oeil.  Parmi  les  couleurs  variees  que 
donne  cet  appareil,  lorsque  de  la  lumiere  polarisee  le  traverse,  et  qu'on 
fait  tourner  le  prisme  sur  lui-meme,  se  trouve  par  un  heureux  basard  la 
nuance  du  bleu  de  ciel.  Cette  couleur  bleue  fort  afiaiblie,  c'est-4-dire 
tres  melangee  de  blanc  lorsque  la  lumiere  est  presque  neutre,  aug- 
mente  d'intensite — progressivement,  a  mesure  que  les  rayons  qui  pene- 
trent  dans  1'instrumeut,  renferment  une  plus  grande  proportion  de  ray- 
ons polarises. 

"  Supposons  done  que  le  polariscope  soit  dirige  sur  une  feuille  de  pa- 
pier blanc ;  qu'entre  cette  feuille  et  la  lame  de  cristal  de  roche  il  ex- 
iste  une  pile  de  plaques  de  verre  susceptible  de  changer  d'inclinaison, 
co  qui  rendra  la  lumiere  eclairante  du  papier  plus  ou  nioins  polarisee ; 
la  couleur  bleue  fournie  par  1'instrument  va  en  augmentant  avec  1'in- 
clinaison  de  la  pile,  et  1'on  s'arrete  lorsque  cette  couleur  parait  la  meme 
que  celle  de  la  region  de  1'atmosphere  dont  on  veut  determiner  la  teinte 
cyanometrique,  et  qu'ou  regarde  &  1'ceil  nu  immecliatement  a  cote  de 
1'instrumeut.  La  mesure  de  cette  teiute  est  don nee  par  1'inclinaison  de 
la  pile.  Si  cette  derniere  partie  de  1'instrument  se  compose  du  meme 
nombre  de  plaques  et  d'une  meme  espece  de  verre,  lea  observations 
faites  dans  divers  lieux  seront  parfaitement  comparables  entr'elles." 

(a.)  Photometric  Measurements. 

"  There  does  not  exist  a  photometer  properly  so  called,  that  is  to 
say,  no  instrument  giving  the  intensity  of  an  isolated  light ;  for  Leslie's 
photometer,  by  means  of  which  he  boldly  supposed  that  he  could  com 
pare  the  light  of  the  moon  with  that  of  the  sun,  by  their  caloric  actions, 
is  utterly  defective.  I  found,  in  fact,  that  this  pretended  photometer 
rose  on  being  exposed  to  the  light  of  the  sun,  that  it  fell  when  exposed 
to  a  moderate  fire,  and  that  it  remained  altogether  stationary  when 
brought  near  the  light  of  an  Argand  lamp.  All  that  has  hitherto  been 
done  has  been  to  compare  two  lights  when  contiguous  to  one  another ; 
but  even  this  comparison  can  not  be  relied  on  unless  the  two  lights  be 
equalized,  the  stronger  being  gradually  reduced  to  the  intensity  of  the 
feebler.  For  the  purpose  of  judging  of  this  inequality  I  employed  col- 
ored rings.  On  placing  on  one  another  two  lenses  of  a  great  focal 
length,  colored  rings  wdl  be  formed  round  their  point  of  contact  as 
much  by  means  of  reflection  as  of  transmission.  The  colors  of  the  r& 
VOL,  III— E 


98  COSMOS. 

The  so-called  relations  of  the  magnitude  cf  the  fixed  star* 
as  given  in  our  catalogues  and  maps  of  the  stars,  sometimes 
indicate  as  of  simultaneous  occurrence  that  which  belongs  to 
very  different  periods  of  cosmical  alterations  of  light.  The 
order  of  the  letters  which,  since  the  beginning  of  the  seven- 
teenth century,  have  been  added  to  the  stars  in  the  general- 
ly consulted  Uranometria  Bayeri,  are  not,  as  was  long  sup- 
posed, certain  indications  of  these  alterations  of  light.  Arge- 
lander  has  ably  shown  that  the  relative  brightness  of  the 
stars  can  not  be  inferred  from  the  alphabetical  order  of  the 
letters,  and  that  Bayer  was  influenced  in  his  choice  of  these 
letters  by  the  form  and  direction  of  the  constellations.* 

fleeted  rings  are  complementary  to  those  of  the  transmitted  rings ;  these 
two  series  of  rings  neutralize  one  another  when  the  two  lights  by  which 
they  aro  formed,  and  which  fall  simultaneously  on  the  two  lenses,  are 
equal. 

"  In  the  contrary  case,  we  meet  with  traces  of  reflected  or  transmit- 
ted rings,  according  as  the  light  by  which  the  former  are  produced  is 
stronger  or  fainter  than  that  from  which  the  latter  are  formed.  It  is 
only  in  this  manner  that  colored  rings  can  ba  said  to  come  into  play  in 
those  photometric  measurements  to  which  I  bavi  diracted  my  atten- 
tion." 

(b.)  Cyanometer. 

"  My  cyanometer  is  an  extension  of  my  polariscope.  This  latter  in- 
strument, as  you  know,  consists  of  a  tube  closed  at  ono  end  by  a  plate 
of  rock  crystal,  cut  perpendicular  to  its  axis,  and  5  millimetres  in  thick- 
ness ;  and  of  a  double  refracting  prism  placed  near  the  part  to  which 
the  eye  is  applied.  Among  the  varied  colors  yielded  by  this  apoaratus, 
when  it  is  traversed  by  polarized  light  and  the  prism  turns  on  itself,  wo 
fortunately  find  a  shade  of  azure.  This  blue,  which  is  very  faint,  that 
is  to  say,  mixed  with  a  large  quantity  of  white  when  the  light  is  almost 
neutral,  gradually  increases  in  intensity  in  proportion  to  the  quantity  of 
polarized  rays  which  enter  the  instrument. 

"  Let  us  suppose  the  polariscope  directed  toward  a  sheet  of  white 
paper,  and  that  between  this  paper  and  the  plate  of  rock  crystal  there 
is  a  pile  of  glass  plates  capable  of  being  variously  inclined,  by  which 
means  the  illuminating  light  of  the  paper  would  be  more  or  less  polar- 
ized ;  the  blue  color  yielded  by  the  instrument  will  go  on  increasing 
•with  the  inclination  of  the  pile ;  and  the  process  must  be  continued  un- 
til the  color  appears  of  the  same  intensity  with  the  region  of  the  atmos- 
phere whose  cyanometrical  tinge  is  to  be  determined,  and  which  is 
seen  by  the  naked  eye  in  the  immediate  vicinity  of  the  instrument. 
The  amount  of  this  color  is  given  by  the  inclination  of  the  pile  ;  and  if 
this  portion  of  the  apparatus  consist  of  the  same  number  of  plates  formed 
of  the  same  kind  of  glass,  observations  made  at  different  places  may 
readily  be  compared  together." 

*  Argelander,  Defde  Uranomelria:  Bayeri,  1842,  p.  14-23.  "In  ea- 
dem  classe  littera  prior  majorem  splendorem  nullo  modo  indicat"  (§ 
9).  Bayer  did  not,  therefore,  show  that  the  light  of  Castor  was  more 
intense  in  1603  than  that  of  Pollux. 


PHOTOMETRIC    SCALE.  99 


PHOTOMETRIC  ARRANGEMENT  OF  THE  FIXED  STARS. 

I  close  this  section  with  a  table  taken  from  Sir  John  Herschel's  Out 
ines  of  Astronomy,  p.  645  and  64G.  I  am  indebted  for  the  mode  of  its 
arrangement,  and  for  the  following  lucid  exposition,  to  my  learned 
friend  Dr.  Galle,  from  whose  communication,  addressed  to  me  in  March, 
1850,  I  extract  the  subjoined  observations : 

"  The  numbers  of  the  photometric  scale  in  the  Outlines  of  Astron- 
omy have  been  obtained  by  adding  throughout  0-41  to  the  results  calcu- 
lated from  the  vulgar  scale.  Sir  John  Herschel  arrived  at  these  more 
exact  determinations  by  observing  their  "  sequences"  of  brightness,  and 
by  combining  these  observations  with  the  average  ordinary  data  of  mag- 
nitudes, especially  on  those  given  in  the  catalogue  of  the  Astronomical 
Society  for  the  year  1827.  See  Observ.  at  the  Cape,  p.  304-352.  The 
actual  photometric  measurements  of  several  stars  as  obtained  by  the 
Astrometer  (op.  cit.,  p.  353),  have  not  been  directly  employed  in  this 
catalogue,  but  have  only  served  generally  to  show  the  relation  existing 
between  the  ordinary  scale  (of  1st,  2d,  3d,  &c.,  magnitudes)  to  the  act- 
ual photometric  quantities  of  individual  stars.  This  comparison  has 
given  the  singular  result  that  our  ordinary  stellar  magnitudes  ( 1, 2, 3  . . .) 
decrease  in  about  the  same  ratio  as  a  star  of  the  first  magnitude  when 
removed  to  the  distances  of  1,  2,  3  ...  by  which  its  brightness,  accord- 
ing to  photometric  law,  would  attain  the  values  1,  Jth,  ^th,  -pg-th  .  .  . 
(Observ.  at  the  Cape,  p.  371,  372  ;  Outlines,  p.  521,  522) ;  in  order,  how- 
ever, to  make  this  accordance  still  greater,  it  is  only  necessary  to  raise 
our  previously  adopted  stellar  magnitudes  about  half  a  magnitude  (or, 
more  accurately  considered,  0-41),  so  that  a  star  of  the  2-00  magnitude 
would  in  future  be  called  2-41,  and  star  of  2-50  would  become  2-91, 
and  so  forth.  Sir  John  Herschel  therefore  proposes  that  this  "  photo- 
metric" (raised)  scale  shall  in  future  be  adopted  (Observ.  at  the  Cape, 
p.  372,  and  Outlines,  p.  522) — a  proposition  in  which  we  can  not  fail  to 
concur  ;  for  while,  on  the  one  hand,  the  difference  from  the  vulgar  scale 
would  hardly  be  felt  (Observ.  at  the  Cape,  p.  372),  the  table  in  the  Out- 
lines (p.  (>45)  may,  on  the  other  hand,  serve  as  a  basis  for  stars  down 
to  the  fourth  magnitude.  The  determinations  of  the  magnitudes  of  the 
stars  according  to  the  rule,  that  the  brightness  of  the  stars  of  the  first, 
second,  third,  fourth  magnitude  is  exactly  as  1,  jth,  ith,  -p^th  ...  as  is 
now  shown  approximatively,  is  therefore  already  practicable.  Sir  John 
Herschel  employs  a  Centauri  as  the  standard  star  of  the  first  magnitude 
for  his  photometric  scale,  and  as  the  unit  for  the  quantity  of  light  (Out- 
lines, p.  523;  Observ.  at  the  Cape,  p.  372).  If,  therefore,  we  take  the 
square  of  a  star's  photometric  magnitude,  we  obtain  the  inverse  ratio 
of  the  quantity  of  its  light  to  that  of  a  Centauri.  Thus,  for  instance,  if 
K  Orionis  have  a  photometric  magnitude  of  3,  it  consequently  has  ^th 
of  the  light  of  a  Centauri.  The  number  3  would  at  the  same  time  in- 
dicate that  K  Orionis  is  3  times  more  distant  from  us  than  a  Centauri, 
provided  both  stars  be  bodies  of  equal  magnitude  and  brightness.  If 
another  star,  as,  for  instance,  Sirius,  which  is  four  times  as  bright,  were 
chosen  as  the  unit  of  the  photometric  magnitudes  indicating  distances, 
the  above  conformity  to  law  would  not  be  so  simple  and  easy  of  recog- 
nition. It  is  also  worthy  of  notice,  that  the  distance  of  a  Centauri  has 
been  ascertained  with  some  probability,  and  that  this  distance  is  the 
smallest  of  any  yet  determined.  Sir  John  Henchel  demonstrates  (  Out- 
lines, p.  521)  the  inferiority  of  other  scales  to  the  photometric,  which 


100  COSMOS. 

progresses  in  order  of  the  squares,  1,  £th,  £th,  Jffth ...  He  likewise 
treats  of  geometric  progressions,  as,  for  instance,  1, 1,  Jth,  |th, ...  or  1, 
^d,  £th,  ^th.  ....  The  gradations  employed  by  yourself  in  your  ob- 
servations under  the  equator,  during  your  travels  in  America,  are  ar- 
ranged in  a  kind  of  arithmetical  progression  (Recueil  d'Observ.  Atlron., 
vol.  i.,  p.  Ixxi.,  and  Schumacher's  Astron.  Nachr.,  No.  374).  These 
scales,  however,  correspond  less  closely  than  the  photometric  scale  of 
progression  (by  squares)  -with  the  vulgar  scale.  In  the  following  table 
the  190  stars  have  been  given  from  the  Outlines,  without  reference  to 
their  declination,  whether  southern  or  northern,  being  arranged  solely 
in  accordance  with  their  magnitudes." 

List  of  190  stars  from  the  first  to  the  third  magnitude,  arranged  accord- 
ing to  the  determinations  of  Sir  John  Herschel,  giving  the  ordinary 
magnitudes  with  greater  accuracy,  and  likewise  the  magnitudes  in  ac- 
cordance with  his  proposed  photometric  classification : 

STARS  OF  THE  FIRST  MAGNITUDE. 


Star. 

Magnitude. 

Star. 

Magnitude. 

Sirius  

Vulg. 

008 

0-29 
059 
077 
082 
1-0 
10 
1-0 

Phot. 

0-49 

0-70 
1-00 
1-18 
1-23 
1-4 
1-4 
1-4 

a  Orionis  

Vulg. 

1-0 
1-09 
1-1 
1-17 
1-2 
1-2 
1-28 
1-38 

Phot. 

1-43 
150 
15 
1-58 
1-6 
1-6 
1  69 
1-79 

tl  Argus  (Var.) 

a  Eridani 

Canopus 

Aldebaran 

a  Centauri....  .  .  

8  Centauri  

Arcturus 

a  Crucis 

Rigel 

An  tares 

Capella  

a  Aquila?  ......... 

a.  Lyra?  

Spica  

Procyon  

STARS  OF  THE  SECOND  MAGNITUDE. 


Star. 

Magnitude. 

Star. 

Magnitude. 

Fomalhaut 

Vulg.l  Phot 

1-541-95 
1-57  1-98 
1-6    2-0 
1-6    20 
1-66207 
1-73214 
l-84!225 
1-862-27 
1-872-28 
1-90!231 
1-94|235 
1-95236 
1-96:2-37 
2-01242 
2-03  2  44 
2-072-48 
2-082-49 
2182-59 
2-18259 
2-18259 

a  Triang  austr. 

2^ 
2-26 
2-28 
228 
229 
230 
232 
233 
234 
2-36 
2-40 
241 
2-42 
243 
2-45 
2-46 
2-46 
2-48 

M 

Phot. 

264 
2-67 
269 
2-69 
270 
271 
273 
2-74 
275 
2-77 
281 
2-82 
2-83 
284 
2-86 
2-87 
28"" 
289 
291 

ft  Crucis 

e  Sagittarii  

Pollux 

3  Tauri 

Regulus 

Polaris  

a  Gruis  .       ..  ....... 

6  Scorpii  

a  Hydra 

e  Orionis 

6  Canis  

e  Can  is 

a  Pavonis  

y  Leonis 

a  Cygni 

8  Gruis 

Castor 

a  Arietis  ........ 

E  Ursse  (Var  ) 

a  Sagittarii 

a  Ursae  (Var  ) 

6  Argus 

f  Orionis 

£  Ursae  

8  Argus             .   ...  .  . 

8  Andromeda?  

/?  Ceti 

A  Argus      .       ........ 

e  Argus 

i?  Ursae  (Var  ) 

y  Andromedse 

y  Orionis  

PHOTOMETRIC   SCALE. 


STARS  OF  THE  THIRD  MAGNITUDE. 


101 


Masmtmle. 

Magnitude. 

y  Cassiopeiae 

Vulg. 

•J  52 
254 
2-54 
2-57 
2-58 
259 
259 
2-61 
2-62 
2-62 
2  62 
263 
263 
263 
263 
265 
265 
2-68 
269 
2-71 
2-71 
2-72 
2-77 
2-78 
2-80 
280 
2-82 
2-82 
2-85 
2-85 
286 
2-88 

Phot. 

2-93 
2-95 
2-95 
2-98 
2-99 
300 
300 
3-02 
3-03 
3-03 
3-03 
3-04 
3-04 
3-04 
3-04 
306 
3-06 
3-09 
3-10 
3-12 
3-12 
3-13 
3-18 
3-19 
3-21 
3-21 
3-23 
323 
326 
326 
3-27 
'VQ 

f  Sagittarii 

Vulg. 

3-01 
3-01 
302 
305 
3-06 
307 
3-08 
3-08 
3-09 
311 
3-11 
312 
313 
3-14 
3-14 
3-15 
3-17 
3-18 
320 
320 
322 
322 
3-23 
324 
3-26 
3-26 
326 
326 
327 
327 
3-28 
3  28 
3-29 
330 
331 
331 
3-^2 
332 
332 
332 
333 
334 
335 
335 
3-35 
335 
33G 
336 
336 
337 

Phot. 

342 
3-42 
343 
346 
347 
348 
349 
349 
350 
352 
352 
353 
354 
355 
355 
356 
358 
359 
361 
3-61 
3  63 
3-63 
3-64 
365 
3-67 
367 
3-67 
367 
368 
368 
369 
369 
370 
3-71 
372 
372 
373 
373 
373 
373 
374 
375 
3-76 
3  76 
376 
376 
377 
377 
377 
a-78 

a  Andromedae   ..... 

77  Bootis  

6  Centauri 

77  Draconis 

a  Cassiopeiae     ........ 

TT  Ophiuchi  

/3  Canis      

i3  Draconis  

*  Orionis 

3  Librae  

y  Geminorum 

y  Virginis  

i  Orionis       .    . 

u  Argns  .  .  

Algol  (Var  ) 

3  Arietis 

y  Pegasi 

6  Sa^ittarii 

(3  Leonis        

a  Libras  

a  Ophiuchi  ...     ... 

*  Sagittarii  

3  Cassiopeiae 

3  Lupi  

y  Cygni      .                ... 

e  Virginis  1  . 

a  Pegasi 

a  Columbae 

3  Pegasi 

i9-  Aurigae  . 

y  Centauri 

3  Herculis 

a  Coronas 

i    Centauri 

y  Ursae 

6  Capricorni 

e  Scorpii 

6  Corvi 

f  Argus 

a  Can.  ven. 

B  Ursa 

3  Ophiuchi 

Phcenicis 

6  Cygni 

Argus 

e  Persei 

Bootis 

TJ  Tauri 

Lupi 

3  Eridani 

Centauri  

&  Argus  

Canis 

3  Hydri 

Aquarii  

f  Persei  

Scorpii  .  . 

f  Herculis  

Cygni 

E  Corvi 

TI  Ophiuchi  

2893-30 
290331 
290.331 
2913-32 
2  92  3  33 
294335 
2943-35 
2  95  3  36 
296337 
2-96337 
2-973-38 
*-973-38 
298339 
298,339 
2  99  3  40 
2-99340 
3-003-41 
3003-41 

i  Aurigae  

y  Corvi  

y  Urs.  Min  

a  Cephei  

T)  Pegasi  

6  Centauri  

3  Arae  

a  Serpentis  

a  Toucani  

6  Leonis  

3  Caprieorni 

K  Argus  

p  Argus  

3  Corvi 

£  Aquilae 

B  Scorpii  

3  Cygni  

f  Centauri  

y  Persei.. 

C  Ophiuchi  .. 

u  Ursae..   . 

a  Aquani 

Tf  Scorpii 

3  Leporis 

6  Cassiopeias  

y  Lupi  

d  Centauri  
a  Leporis  ............. 

I  Persei  

^  Ursse  

6  Ophiuchi  .. 

e  Aurigae  (Var.)  .. 

102 


Star. 

M^utudp. 

Star. 

MHgmtii.l..-. 

v  Scorpii 

Vulg. 

3-37 
337 
339 
3-40 
340 
340 
3-41 
3-41 
342 
3-42 
3-42 
343 
343 
343 
344 
344 
344 

Phot 

3-78 
3-78 
3-80 
3-81 
381 
3-81 
3-82 
3-82 
383 
383 
383 
3-84 
384 
3-84 
385 
385 
385 

<5  Geminorum 

Z& 

3-45 
3-45 
345 
3-45 
3-46 
346 
3-46 
3-46 
3-47 
348 
348 
349 
349 
350 
350 
3-50 

Phot. 

3-85 
3-86 
386 
3-86 
3-86 
3-87 
3-87 
387 
3-87 
3-88 
389 
389 
3-90 
3-90 
391 
391 
391 

i   Orionis 

o  Orionis  ... 

y  Lyncis 

(3  Cephei  

tfUrsae 

f  Hydra 

rr  Sagittarii      ...... 

y  Hydrae  

TT  Herculis  .  

f3  Triang.  austr  

/3  Can.  min.  1 

t  Ursae 

f  Tauri 

tj  Aurigae     ... 

(5  Draconis  

y  Lyrae  ......... 

p  Geminorum  

T)  Geminorum  

y  Bootis 

y  Cephei 

e  Geminorum 

K  Ursas 

a  Muscae  

e  Cassiopeiae  .... 

a  Hydri? 

1?  Aquilae 

T  Scorpii 

a  Scorpii 

6  Herculis  

r  Argus  

"  The  following  short  table  of  the  photometric  quantities 
of  seventeen  stars  of  the  first  magnitude  (as  obtained  from 
the  photometric  scale  of  magnitudes)  may  not  be  devoid  of 
interest :" 

Sirius 4-165 

7i  Argus 

Canopus 2-041 

aCentauri 1-000 

Arcturus 0-718 

Rigel 0-661 

Capella 0-510 

aLyrae 0-510 

Procyon 0-510 

"  The  following  is  the  photometric  quantity  of  stars  strict- 
ly belonging  to  the  1st,  2d 6th  magnitudes,  in  which 

the  quantity  of  the  light  of  a  Centauri  is  regarded  as  the 
unit :" 


a  Orionis   .... 
a  Eridani  .... 
Aldebaran.  . 
j3  Centauri  .  .  . 
a  Crucis  
Antares  .... 
a  Aquilae  .... 
Spica          .  . 

0-489 
.0-444 
0-444 
0-401 
.0-391 
.0-391 
.0-350 
0-312 

Magnitude  on 
the  vulgar  scale. 

1-00 
2-00 
3-00 


Quantity 
of  light 

0-500 
0-172 
0-086 


Magnitude  on 
the  vulgar  scale. 

4-00 
5-00 
6-00 


Quantity 
of  light. 

0-051 
0-034 
0-024 


III. 

NUMBER,  DISTRIBUTION,  AND  COLOR  OF  THE  FIXED  STARS.  — STEL- 
LAR MASSES  (STELLAR  SWARMS).— THE  MILKY  WAY  INTERSPERSED 
WITH  A  FEW  NEBULOUS  SPOTS. 

We  have  already,  in  the  first  section  of  this  fragmentary 
Astrognosy,  drawn  attention  to  a  question  first  mooted  by 
Olbers.*  If  the  entire  vault  of  heaven  were  covered  with 
innumerable  strata  of  stars,  one  behind  the  other,  as  with  a 
•wide-spread  starry  canopy,  and  light  were  undiminished  in 
its  passage  through  space,  the  sun  would  be  distinguishable 
only  by  its  spots,  the  moon  would  appear  as  a  dark  disk, 
and  amid  the  general  blaze  not  a  single  constellation  would 
be  visible.  During  my  sojourn  in  the  Peruvian  plains,  be- 
tween the  shores  of  the  Pacific  and  the  chain  of  the  Andes, 
I  was  vividly  reminded  of  a  state  of  the  heavens  which, 
though  diametrically  opposite  in  its  cause  to  the  one  above 
referred  to,  constitutes  an  equally  formidable  obstacle  to  hu- 
man knowledge.  A  thick  mist  obscures  the  firmament  in 
this  region  for  a  period  of  many  months,  during  the  season 
called  el  tiempo  de  la  garua.  Not  a  planet,  not  the  most 
brilliant  stars  of  the  southern  hemisphere,  neither  Canopus, 
the  Southern  Cross,  nor  the  feet  of  the  Centaur,  are  visible. 
It  is  frequently  almost  impossible  to  distinguish  the  position 
of  the  moon.  If  by  chance  the  outline  of  the  sun's  disk  be 
visible  during  the  day,  it  appears  devoid  of  rays,  as  if  seen 
through  colored  glasses,  being  generally  of  a  yellowish  red, 
sometimes  of  a  white,  and  occasionally  even  of  a  bluish  green 
color.  The  mariner,  driven  onward  by  the  cold  south  cur- 
rents of  the  sea,  is  unable  to  recognize  the  shores,  and  in  the 
absence  of  all  observations  of  latitude,  sails  past  the  harbors 
which  he  desired  to  enter.  A  dipping  needle  alone  could, 
as  I  have  elsewhere  shown,  save  him  from  this  error,  by  the 
local  direction  of  the  magnetic  curves. f 

Bouguer  and  his  coadjutor,  Don  Jorge  Juan,  complained, 
long  before  me,  of  the  "  unastronomical  sky  of  Peru."  A 
graver  consideration  associates  itself  with  this  stratum  of 
vapors,  in  which  there  is  neither  thunder  nor  lightning,  in 
consequence  of  its  incapacity  for  the  transmission  of  light  or 
electric  charges,  and  above  which  the  Cordilleras,  free  and 
cloudless,  raise  their  elevated  plateaux  and  snow-covered 

*  Vide  supra,  p.  38,  and  note. 

t  Cotmos,  vol.  i.,  p.  178,  and  note. 


104  COSMOS. 

summits.  According  to  what  modern  geology  has  taught  us 
to  conjecture  regarding  the  ancient  history  of  our  atmosphere, 
its  primitive  condition,  in  respect  to  its  mixture  and  density, 
must  have  been  unfavorable  to  the  transmission  of  light. 
When  we  consider  the  numerous  processes  which,  in  the  pri- 
mary world,  may  have  led  to  the  separation  of  the  solids, 
fluids,  and  gases  around  the  earth's  surface,  the  thought  in- 
voluntarily arises  how  narrowly  the  human  race  escaped  be- 
ing surrounded  with  an  untransparent  atmosphere,  which, 
though  perhaps  not  greatly  prejudicial  to  some  classes  of 
vegetation,  would  yet  have  completely  veiled  the  whole  of 
the  starry  canopy.  All  knowledge  of  the  structure  of  the 
universe  would  thus  have  been  withheld  from  the  inquiring 
spirit  of  man.  Excepting  our  own  globe,  and  perhaps  the 
sun  and  the  moon,  nothing  would  have  appeared  to  us  to 
have  been  created.  An  isolated  triad  of  stars — the  sun,  the 
moon,  and  the  earth — would  have  appeared  the  sole  occu- 
pants of  space.  Deprived  of  a  great,  and,  indeed,  of  the  sub- 
limest  portion  of  his  ideas  of  the  Cosmos,  man  would  have 
been  left  without  all  those  incitements  which,  for  thousands 
of  years,  have  incessantly  impelled  him  to  the  solution  of 
important  problems,  and  have  exercised  so  beneficial  an  in- 
fluence on  the  most  brilliant  progress  made  in  the  higher 
spheres  of  mathematical  development  of  thought.  Before 
we  enter  upon  an  enumeration  of  what  has  already  been 
achieved,  let  us  dwell  for  a  moment  on  the  danger  from 
which  the  spiritual  development  of  our  race  has  escaped,  and 
the  physical  impediments  which  would  have  formed  an  im- 
passable barrier  to  our  progress. 

In  considering  the  number  of  cosmical  bodies  which  fill 
the  celestial  regions,  three  questions  present  themselves  to 
our  notice.  How  many  fixed  stars  are  visible  to  the  naked 
eye  ?  How  many  of  these  have  been  gradually  catalogued, 
and  their  places  determined  according  to  longitude  and  lat- 
itude, or  according  to  their  right  ascension  and  declination  ? 
"What  is  the  number  of  stars  from  the  first  to  the  ninth  and 
tenth  magnitudes  which  have  been  seen  in  the  heavens  by 
means  of  the  telescope  ?  These  three  questions  may,  from 
the  materials  of  observation  at  present  in  our  possession, 
be  determined  at  least  approximatively.  Mere  conjectures 
based  on  the  gauging  of  the  stars  in  certain  portions  of  the 
Milky  Way,  differ  from  the  preceding  questions,  and  refer  to 
the  theoretical  solution  of  the  question :  How  many  stars 
might  be  distinguished  throughout  the  whole  heavens  with 


NUMBER    OF    THE   FIXED    STARS.  105 

Herschel's  twenty-feet  telescope,  including  the  stellar  light, 
"  which  is  supposed  to  require  2000  years  to  reach  oui 
earth  ?"* 

The  numerical  data  which  I  here  publish  in  reference  to 
this  subject  are  chiefly  obtained  from  the  final  results  of  my 
esteemed  friend  Argelander,  director  of  the  Observatory  at 
Bonn.  I  have  requested  the  author  of  the  Durchmusterung 
des  nordlichen  Himmeh  (Suney  of  the  Northern  Heav- 
ens) to  submit  the  previous  results  of  star  catalogues  to  a 
new  and  careful  examination.  In  the  lowest  class  of  stars 
visible  to  the  naked  eye,  much  uncertainty  arises  from  or- 
ganic difference  in  individual  observations  ;  stars  between 
the  sixth  and  seventh  magnitude  being  frequently  confound- 
ed with  those  strictly  belonging  to  the  former  class.  We 
obtain,  by  numerous  combinations,  from  5000  to  5800  as  the 
mean  number  of  the  stars  throughout  the  whole  heavens  vis- 
ible to  the  unaided  eye.  Argelanderf  determines  the  distri- 

*  On  the  space-penetrating  power  of  telescopes,  see  Sir  John  Her- 
schel,  Outlines  of  Astr.,  §  803. 

t  I  can  not  attempt  to  include  in  a  note  all  the  grounds  on  which 
Argelander's  views  are  based.  It  will  suffice  if  I  extract  the  following 
remarks  from  his  own  letters  to  me:  "Some  years  since  (1843)  you 
recommended  Captain  Schwink  to  estimate  from  his  Mappa  Coelestis 
the  total  number  of  stars  from  the  first  to  the  seventh  magnitude  in- 
clusive, which  the  heavens  appeared  to  contain ;  his  calculations  give 
12,1 48  stars  for  the  space  between  30°  south  and  90°  north  declination ; 
and  consequently,  if  we  conjecture  that  the  proportion  of  stars  is  the 
same  from  30°  S.  D.  to  the  South  Pole,  we  should  have  16,200  stars  of 
the  above-named  magnitudes  throughout  the  whole  firmament.  This 
estimate  seems  to  me  to  approximate  very  nearly  to  the  truth.  It  is 
well  known  that,  on  considering  the  whole  mass,  we  find  each  class 
contains  about  three  times  as  many  stars  as  the  one  preceding.  (Struve, 
Catalogvs  Sldlarum  duplicium,  p.  xxxiv. ;  Argelander,  Banner  Zonen, 
s.  xxvi.)  I  have  given  in  my  Uranometria  1441  stars  of  the  sixth  mag- 
nitude north  of  the  equator,  whence  we  should  obtain  about  3000  for 
the  whole  heavens;  this  estimate  does  not,  however,  include  the  stars 
of  the  6-7  mag.,  which  would  be  reckoned  among  those  of  the  sixth,  if 
only  entire  classes  were  admitted  into  the  calculation.  I  think  the 
number  of  the  last-named  stars  might  be  assumed  at  1000,  according 
to  the  above  rule,  which  would  give  4000  stars  for  the  sixth,  and  12  000 
for  the  seventh,  or  18,000  for  the  first  to  the  seventh  inclusive.  From 
other  considerations  on  the  number  of  the  stars  of  the  seventh  magni- 
tude, as  given  in  my  zones — namely,  2257  (p.  xxvi.),  and  allowing  for 
those  which  have  been  twice  or  oftener  observed,  and  for  those  which 
have  probably  been  overlooked,  I  approximated  somewhat  more  nearly 
to  the  truth.  By  this  method  I  found  2340  stars  of  the  seventh  magni- 
tude between  45°  and  80°  N.  D.,  and,  therefore,  nearly  17,000  for  the 
whole  heavens.  Struve,  in  his  Description  de  V  Observatoire  de  Paul- 
kova,  p.  268,  gives  13,400  for  the  number  of  stars  down  to  the  seventh 
magnitude  in  the  region  of  the  heavens  explored  by  him  (from  — 15° 
E  2 


106  COSMOS. 

bution  of  the  fixed  stars  according  to  difference  of  magnitude, 
down  to  the  ninth,  in  about  the  following  proportion  . 

to  +90°),  whence  we  should  obtain  21,300  for  the  whole  firmament. 
According  to  the  introduction  to  Weisse's  Catal.  e  Zonis  Regiomonta- 
nit,  dcd.,  p.  xxxii.,  Struve  found  in  the  zone  extending  from  — 15°  to 
-{-15°  by  the  calculus  of  probabilities,  3903  stars  from  the  first  to  the 
seventh,  and  therefore  15,050  for  the  entire  heavens.  This  number  is 
lower  than  mine,  because  Bessel  estimated  the  brighter  stars  nearly 
half  a  magnitude  lower  than  I  did.  We  can  here  only  arrive  at  a  mean 
result,  which  would  be  about  18,000  from  the  first  to  the  seventh  mag- 
nitudes inclusive.  Sir  John  Herschel,  in  the  passage  of  the  Outlines  of 
Astronomy,  p.  521,  to  which  you  allude,  speaks  only  of  '  the  whole  num- 
ber of  stars  already  registered,  down  to  the  seventh  magnitude  inclu- 
sive, amounting  to  from  12,000  to  15,000.'  As  regards  the  fainter  stars, 
Struve  finds  within  the  above-named  zone  (from  — 15°  to  +15°),  for 
the  faint  stars  of  the  eighth  magnitude,  ]  0,557  ;  for  those  of  the  ninth, 
37,739 ;  and,  consequently,  40,800  stars  of  the  eighth,  and  145,800  of  the 
ninth  magnitude  for  the  whole  heavens.  Hence,  according  to  Struve, 
we  have,  from  the  first  to  the  ninth  magnitude  inclusive,  15,100+ 
40,800+145,800=201,700  stars.  He  obtained  these  numbers  by  a 
careful  comparison  of  those  zones  or  parts  of  zones  which  comprise  the 
same  regions  of  the  heavens,  deducing  by  the  calculus  of  probabilities 
the  number  of  stars  actually  present  from  the  numbers  of  those  com- 
mon to,  or  different  in,  each  zone.  As  the  calculation  was  made  from 
a  very  large  number  of  stars,  it  is  deserving  of  great  confidence.  Bes- 
sel  has  enumerated  about  61,000  different  stars  from  the  first  to  the 
ninth  inclusive,  in  his  collective  zones  between  — 15°  and  +45°,  after 
deducting  such  stars  as  have  been  repeatedly  observed,  together  with 
those  of  the  9-10  magnitude;  whence  we  may  conclude,  after  taking 
into  account  such  as  have  probably  been  overlooked,  that  this  portion 
of  the  heavens  contains  about  101,500  stars  of  the  above-named  magni- 
tudes. My  zones  between  -j-45°  and  -|-80°  contain  about  22,000  stars 
(Durchmu  sterung  des  ndrdl.  Himmels,  s.  xxv.),  which  would  leave  about 
19,000  after  deducting  3000  for  those  belonging  to  the  9-10  magnitude. 
My  zones  are  somewhat  richer  than  Bessel's,  and  I  do  not  think  we  can 
fairly  assume  a  larger  number  than  2850  for  the  stars  actually  existing 
between  their  limits  (+45°  and  +80°),  whence  we  should  obtain 
130,000  stars  to  the  ninth  magnitude  inclusive,  between  — 15°  and 
-J-800.  This  space  is,  however,  only  0-62181  of  the  whole  heavens, 
and  we  therefore  obtain  209,000  stars  for  the  entire  number,  supposing 
an  equal  distribution  to  obtain  throughout  the  whole  firmament ;  these 
numbers,  again,  closely  approximate  to  Struve's  estimate,  and,  indeed, 
not  improbably  exceed  it  to  a  considerable  ttent,  since  Struve  reck- 
oned stars  of  the  9-10  magnitude  among  thosrof  the  ninth.  The  num- 
bers which,  according  to  my  view,  may  be  ashamed  for  the  whole  firm- 
ament, are  therefore  as  follows :  first  mag.,  20  ;  second,  65  ;  third,  190 ; 
fourth,  425;  fifth,  1100;  sixth,  3200;  seventh,  13,000;  eighth,  40,000; 
ninth,  142,000 ;  and  200,000  for  the  entire  number  of  stars  from  the 
first  to  the  ninth  magnitude  inclusive. 

If  you  would  contend  that  Lalande  {Hist.  Celeste,  p.  iv.)  has  given 
the  number  of  stars  observed  by  himself  with  the  naked  eye  at  6000,  I 
would  simply  remark  that  this  estimate  contains  very  many  that  have 
been  repeatedly  observed,  and  that  after  deducting  these,  we  obtain 
only  about  3800  stars  for  the  portion  of  the  heavens  between  — 26°  30* 


NUMBER   OF    THH    FIXED    STARS.  107 

1st  Mag.  SdMag.  3d  Mag.  4th  Mag.  5th  Mag. 

20  65  190  425  1100 

6th  Mag.  7th  Mag.  8th  Mag.  9th  Mag. 

3200  13,000  40,000  142,000 
The  number  of  stars  distinctly  visible  to  the  naked  eye 
(amounting  in  the  horizon  of  Berlin  to  4022,  and  in  that  of 
Alexandria  to  4638)  appears  at  first  sight  strikingly  small.* 
If  we  assume  the  moon's  mean  semi-diameter  at  15'  33"' 5, 
it  would  require  195,291  surfaces  of  the  full  moon  to  cover 
the  whole  heavens.  If  we  further  assume  that  the  stars  are 
uniformly  distributed,  and  reckon  in  round  numbers  200,000 
stars  from  the  first  to  the  ninth  magnitude,  we  shall  have 
nearly  a  single  star  for  each  full-moon  surface.  This  result 
explains  why,  also,  at  any  given  latitude,  the  moon  does  not 
more  frequently  conceal  stars  visible  to  the  naked  eye.  If  the 
calculation  of  occultations  of  the  stars  were  extended  to  those 
of  the  ninth  magnitude,  a  stellar  eclipse  would,  according  to 
Galle,  occur  on  an  average  every  44'  30",  for  in  this  period 
the  moon  traverses  a  portion  of  the  heavens  equal  in  extent 
to  its  own  surface.  It  is  singular  that  Pliny,  who  was  un- 
doubtedly acquainted  with  Hipparchus's  catalogue  of  stars, 

and  +90°  observed  by  Lalande.  As  this  space  is  0  723 1 0  of  the  whole 
heavens,  we  should  again  have  for  this  zone  5255  stars  visible  to  the 
naked  eye.  An  examination  of  Bode's  Uranography  (containing  17,240 
stars),  which  is  composed  of  the  most  heterogeneous  elements,  does  not 
give  more  than  5600  stars  from  the  first  to  the  sixth  magnitude  inclusive, 
after  deducting  the  nebulous  spots  and  smaller  stars,  as  well  as  those 
of  the  G-7th  magnitude,  which  have  been  raised  to  the  sixth.  A  simi- 
lar estimate  of  the  stars  registered  by  La  Caille  between  the  south  pole 
and  the  tropic  of  Capricorn,  and  varying  from  the  first  to  the  sixth  mag- 
nitude, presents  for  the  whole  heavens  two  limits  of  3960  and  5900,  and 
thus  confirms  the  mean  result  already  given  by  yourself.  You  will 
perceive  that  I  have  endeavored  to  fulfill  your  wish  for  a  more  thor- 
ough investigation  of  these  numbers,  and  I  may  further  observe  that  M. 
Heis,  of  Aix-la-Chapelle,  has  for  many  years  been  engaged  in  a  very 
careful  revision  of  my  Uranometrie.  From  the  portions  of  this  work 
already  complete,  and  from  the  great  additions  made  to  it  by  an  observ 
er  gifted  with  keener  sight  than  myself,  I  find  2836  stars  from  the  first 
to  the  sixth  magnitude  inclusive  for  the  northern  hemisphere,  and  there- 
fore, on  the  presupposition  of  equal  distribution,  5672  as  the  number 
of  stars  visible  throughout  the  whole  firmament  to  the  keenest  unaided 
vision."  {From  the  Manuscripts  of  Professor  Argelander,  March,  1850.) 
*  Schubert  reckons  the  number  of  stare,  from  the  first  to  the  sixth 
magnitude,  at  7000  for  the  whole  heavens  (which  closely  approximates 
to  the  calculation  made  by  myself  in  Cosmos,  vol.  i.,  p.  150),  and  up- 
ward of  5000  for  the  horizon  of  Paris.  He  gives  70,000  for  the  whole 
sphere,  including  stars  of  the  ninth  magnitude.  (Astronomic,  th.  in.,  s. 
54.)  These  numbers  are  all  much  too  high.  Argelander  finds  only 
58,000  from  the  first  to  the  eighth  magnitude. 


108  COSMOS. 

and  who  comments  on  his  boldness  in  attempting,  as  it  were, 
"  to  leave  heaven  as  a  heritage  to  posterity,"  should  have 
enumerated  only  1600  stars  visible  in  the  fine  sky  of  Italy  !* 
In  this  enumeration  he  had,  however,  descended  to  stars  of 
the  fifth,  while  half  a  century  later  Ptolemy  indicated  only 
1025  stars  down  to  the  sixth  magnitude. 

Since  it  has  ceased  to  be  the  custom  to  class  the  fixed  stars 
merely  according  to  the  constellations  to  which  they  belong, 
and  they  have  been  catalogued  according  to  determinations 
of  place,  that  is,  in  their  relations  to  the  great  circles  of  the 
equator  or  the  ecliptic,  the  extension  as  well  as  the  accuracy 
of  star  catalogues  has  advanced  with  the  progress  of  science 
and  the  improved  construction  of  instruments.  No  catalogues 
of  the  stars  compiled  by  Timocharis  and  Aristyllus  (283  B.C.) 
have  reached  us ;  but  although,  as  Hipparchus  remarks  in 
the  fragment  "  on  the  length  of  the  year,"  cited  in  the  sev- 
enth book  of  the  Almagest  (cap.  3,  p.  xv.,  Halma),  their  ob- 
servations were  conducted  in  a  very  rough  manner  (navv 
oAoo^epoif),  there  can  be  no  doubt  that  they  both  determ- 
ined the  declination  of  many  stars,  and  that  these  determin- 
ations preceded  by  nearly  a  century  and  a  half  the  table  of 
fixed  stars  compiled  by  Hipparchus.  This  astronomer  is  said 
to  have  been  incited  by  the  phenomenon  of  a  new  star  to 
attempt  a  survey  of  the  whole  firmament,  and  endeavor  to 
determine  the  position  of  the  stars ;  but  the  truth  of  this 
statement  rests  solely  on  Pliny's  testimony,  and  has  often 
been  regarded  as  the  mere  echo  of  a  subsequently  invented 
tradition.!  It  does  indeed  seem  remarkable  that  Ptolemy 
should  not  refer  to  the  circumstance,  but  yet  it  must  be  ad- 
mitted that  the  sudden  appearance  of  a  brightly  luminous 

*  "  Patrocinatur  vastitas  cceli,  immensa  discreta  altitudine,  in  duo  at- 
que  septuaginta  signa.  Haec  sunt  rerum  et  animantium  effigies,  in  quas 
digessere  ccelum  periti.  In  his  quidem  mille  sexcentas  adnotavere  stel- 
las, iusignes videlicet effectu visuve"  ....  Plin., ii., 41.  "Hipparchus 
nunquam  satis  laudatus,  ut  quo  nemo  magis  approbaverit  cognationera 
cum  homine  siderum  animasque  nostras  partem  esse  coeli,  novam  stel 
lam  et  aliam  in  aevo  suo  genitam  deprehendit,  ejusque  motu,  qua  die 
fulsit,  ad  dubitationem  est  adductus,  anne  hoc  saepius  fieret  moveren- 
turque  et  ese  quas  putamus  affixas ;  itemque  ausus  rem  etiam  Deo  im- 
probam,  adnumerare  posteris  Stellas  ac  sidera  ad  nomen  expungere,  or- 
ganis  excogitatis,  per  quse  singularum  loca  atque  magnitudines  signaret, 
ut  facile  discerni  posset  ex  eo,  non  modo  an  obirent  nascerenturve,  sed 
an  omnino  aliqua  transirent  moverenturve,  item  an  crescerent  minue- 
renturque,  coelo  in  hereditate  cunctis  relicto,  si  quisquam  qvi  cretioneru 
earn  caperet  inventus  esset." — Plin.,  ii.,  26. 

t  Delambre,  Hist,  de  VAstr.  Anc.,  torn,  i.,  p.  290,  and  Hist,  de  VAstr. 
Mod.,  torn,  ii.,  p.  186. 


NUMBER    OF   THE    FIXED    STARS.  109 

star  in  Cassiopeia  (November,  1572)  led  Tycho  Brahe  to 
compose  his  catalogue  of  the  stars.  According  to  an  ingen- 
ious conjecture  of  Sir  John  Herschel,*  the  star  referred  to  by 
Pliny  may  have  been  the  new  star  which  appeared  in  Scorpio 
in  the  month  of  July  of  the  year  134  before  our  era  (as  we 
learn  from  the  Chinese  Annals  of  the  reign  of  "Wou-ti,  of  the 
Han  dynasty).  Its  appearance  occurred  exactly  six  years 
before  the  epoch  at  which,  according  to  Ideler's  investiga- 
tions, Hipparchus  compiled  his  catalogue  of  the  stars.  Ed- 
ward Biot,  whose  early  death  proved  so  great  a  loss  to  science, 
found  a  record  of  this  celestial  phenomenon  in  the  celebra- 
ted collection  of  Ma-tuan-lin,  which  contains  an  account  of 
all  the  comets  and  remarkable  stars  observed  between  the 
years  B.C.  613  and  A.D.  1222. 

The  tripartite  didactic  poem  of  Aratus,t  to  whom  we  are 
indebted  for  the  only  remnant  of  the  works  of  Hipparchus 
that  has  come  down  to  us,  was  composed  about  the  period  of 
Eratosthenes,  Timocharis,  and  Aristyllus.  The  astronomical 
non-meteorological  portion  of  the  poem  is  based  on  the  ura- 
nography  of  Eudoxus  of  Cnidos.  The  catalogue  compiled  by 
Hipparchus  is  unfortunately  not  extant ;  but,  according  to 
Ideler,f  it  probably  constituted  the  principal  part  of  his  work, 
cited  by  Suidas,  "  On  the  arrangement  of  the  region  of  the 
fixed  stars  and  the  celestial  bodies,"  and  contained  1080  de- 
terminations of  position  for  the  year  B.C.  128.  In  Hippar- 
chus's  other  Commentary  on  Aratus,  the  positions  of  the  stars, 
which  are  determined  more  by  equatorial  armillse  than  by 
the  astrolabe,  are  referred  to  the  equator  by  right  ascension 
and  declination  ;  while  in  Ptolemy's  catalogue  of  stars,  which 
is  supposed  to  have  been  entirely  copied  from  that  of  Hip- 
parchus, and  which  gives  1025  stars,  together  with  five  so- 
called  nebulae,  they  are  referred  by  longitudes  and  latitudes 

*  Outlines,  $  831 ;  Edward  Biot,  Sur  les  Etoilet  Extraordinaire*  ob- 
servles  en  Chine,  in  the  Connaissance  des  temps  pour  1846. 

t  It  is  worthy  of  remark  that  Aratus  was  mentioned  with  approba- 
tion almost  simultaneously  by  Ovid  (Amor.,  i.,  15)  and  by  the  Apostle 
Paul  at  Athens,  in  an  earnest  discourse  directed  against  the  Epicureans 
•and  Stoics.  Paul  (Acts,  ch.  xvii.,  v.  28),  although  he  does  not  mention 
Aratus  by  name,  undoubtedly  refers  to  a  verse  composed  by  him  (Phccn., 
v.  5)  on  the  close  communion  of  mortals  with  the  Deity. 

\  Ideler,  Untersuchungen  fiber  den  Unsprung  der  Stemnamen,  s.  xxx.— 
xxxv.  Daily,  in  the  Mem.  of  the  Astron.  Soc.,  vol.  xiii.,  1843,  p.  12  and 
15,  also  treats  of  the  years  according  to  our  era,  to  which  we  must  refer 
the  observations  of  Aristyllus,  as  well  as  the  catalogues  of  the  stars  com- 
piled by  Hipparchus  (128.  and  not  140,  B.C.)  and  by  Ptolemy  (138 
AD.). 


110  COSMOS. 

to  the  ecliptic.*  On  comparing  the  number  of  fixed  stars  m 
the  Hipparcho-Ptolemaic  Catalogue,  Almagest,  ed.  Halma, 
t.  ii.,  p.  83  (namely,  for  the  first  mag.,  15  stars  ;  second,  45  ; 
third,  208  ;  fourth,  474  ;  fifth,  217  ;  sixth,  49),  with  the 
numbers  of  Argelander  as  already  given,  we  find,  as  might 
be  expected,  a  great  paucity  of  stars  of  the  fifth  and  sixth 
magnitudes,  and  also  an  extraordinarily  large  number  of 
those  belonging  to  the  third  and  fourth.  The  vagueness  in 
the  determinations  of  the  intensity  of  light  in  ancient  and 
modern  times  renders  direct  comparisons  of  magnitude  ex- 
tremely uncertain. 

Although  the  so-called  Ptolemaic  catalogue  of  the  fixed 
stars  enumerated  only  one  fourth  of  those  visible  to  the  naked 
eye  at  Rhodes  and  Alexandria,  and,  owing  to  erroneous  re- 
ductions of  the  precession  of  the  equinoxes,  determined  their 
positions  as  if  they  had  been  observed  in  the  year  63  of  our 
era,  yet,  throughout  the  sixteen  hundred  years  immediately 
following  this  period,  we  have  only  three  original  catalogues 
of  stars,  perfect  for  their  time ;  that  of  Ulugh  Beg  (1437), 

*  Compare  Delambre,  Hist,  de  I'Astr.  Anc.,  torn,  i.,  p.  184;  torn,  ii., 
p.  260.  The  assertion  that  Hipparchus,  in  addition  to  the  right  ascen- 
sion and  declination  of  the  stars,  also  indicated  their  positions  in  his 
catalogue,  according  to  longitude  and  latitude,  as  was  done  by  Ptolemy, 
is  wholly  devoid  of  probability  and  in  direct  variance  with  the  Alma- 
gest, book  vii.,  cap.  4,  where  this  reference  to  the  ecliptic  is  noticed  as 
something  new,  by  which  the  knowledge  of  the  motions  of  the  fixed 
stars  round  the  pole  of  the  ecliptic  may  be  facilitated.  The  table  of 
stars  with  the  longitudes  attached,  which  Petrus  Victorius  found  in  a 
Medicean  Codex,  and  published  with  the  life  of  Aratus  at  Florence  in 
1567,  is  indeed  ascribed  by  him  to  Hipparchus,  but  without  any  proof. 
It  appears  to  be  a  mere  rescript  of  Ptolemy's  catalogue  from  an  old 
manuscript  of  the  Almagest,  and  does  not  give  the  latitudes.  As  Ptole- 
my was  imperfectly  acquainted  with  the  amount  of  the  retrogression  of 
the  equinoctial  and  solstitial  points  (Almag.,  vii.,  c.  2,  p.  13,  Halma), 
and  assumed  it  about  T^  too  slow,  the  catalogue  which  he  determined 
for  the  beginning  of  tne  reign  of  Antoninus  (Ideler,  op.  cit.,  B.  xxxiv.) 
indicates  the  positions  of  the  stars  at  a  much  earlier  epoch  (for  the  year 
63  A.D.).  (Regarding  the  improvements  for  reducing  stars  to  the  time 
of  Hipparchus,  see  the  observations  and  tables  as  given  by  Encke  in 
Schumacher's  Astron.  Nachr.,  No.  608,  s.  113-126.)  The  earlier  epoch 
to  which  Ptolemy  unconsciously  reduced  the  stars  in  his  catalogue  cor- 
responds tolerably  well  with  the  period  to  which  we  may  refer  the 
Pseudo-Eratosthenian  Catasterisms,  which,  as  I  have  already  elsewhere 
observed,  are  more  recent  than  the  time  of  Hyginus,  who  lived  in  the 
Augustine  age,  but  appear  to  be  taken  from  him,  and  have  no  connec- 
tion with  the  poem  of  Hermes  by  the  true  Eratosthenes.  (Eratostheni- 
ea,  ed.  Bernhardy,  1822,  p.  114,  116,  129.)  These  Pseudo-Eratosthe- 
nian Catasterisms  contain,  moreover,  scarcely  700  individual  stars  dis- 
tributed among  the  mythical  constellations. 


EARLY  CATALOGUES.  -Ill 

that  of  Tycho  Brahe  (1600),  and  that  of  Hevelius  (1660). 
During  the  short  intervals  of  repose  which,  amid  tumultuous 
revolutions  and  devastations  of  war,  occurred  between  the 
ninth  and  fifteenth  centuries,  practical  astronomy,  under 
Arabs,  Persians,  and  Moguls  (from  Al-Mamun,  the  son  of  the 
great  Haroun  Al-Raschid,  to  the  Timurite,  Mohammed  Tar- 
aghi  Ulugh  Beg,  the  son  of  Shah  Rokh),  attained  an  emi- 
nence till  then  unknown.  The  astronomical  tables  of  Ebn- 
Junis  (1007),  called  the  Hakemitic  tables,  in  honor  of  the 
Fatimite  calif,  Aziz  Ben-Hakem  Biamrilla,  afford  evidence, 
as  do  also  the  Ilkhanic  tables*  of  Nassir-Eddin  Tusi  (who 
founded  the  great  observatory  at  Meragha,  near  Tauris,  1259), 
of  the  advanced  knowledge  of  the  planetary  motions — the 
improved  condition  of  measuring  instruments,  and  the  mul- 
tiplication of  more  accurate  methods  differing  from  those  em- 
ployed by  Ptolemy.  In  addition  to  clepsydras,f  pendulum- 
oscillationsj  were  already  at  this  period  employed  in  the 
measurement  of  time. 

The  Arabs  had  the  great  merit  of  showing  how  tables 
might  be  gradually  amended  by  a  comparison  with  observa- 
tions. Ulugh  Beg's  catalogue  of  the  stars,  originally  written 
in  Persian,  was  entirely  completed  from  original  observations 
made  in  the  Gymnasium  at  Samarcand,  with  the  exception 
of  a  portion  of  the  southern  stars  enumerated  by  Ptolemy,  4 

*  Cosmos,  vol.  ii.,  p.  222,  223.  The  Paris  Library  contains  a  manu- 
script of  the  Ilkhanic  Tables  by  the  hand  of  the  son  of  Nassir-Eddin. 
They  derive  their  name  from  the  title  "  Ilkhan,"  assumed  by  the  Tar- 
tar princes  who  held  rule  in  Persia. — Reinaud,  Introd.  de  la  Gfogr. 
d'Aboulfeda,  1848,  p.  cxxxix. 

t  [For  an  account  of  clepsydras,  see  Beckmann's  Inventions,  voL  i., 
341,  et  seq.  (Bohn's  edition).]— Ed. 

t  Sedillot  fils,  Prolegomenes  des  Tables  Astr.  d' Oloug-Beg,  1847,  p. 
cxxxiv.,  note  2.  Delambre,  Hist,  de  I' Astr.  du  May  en  Age,  p.  8. 

$  In  my  investigations  on  the  relative  value  of  astronomical  determ- 
inations of  position  in  Central  Asia  (Asie  Centrale,  t.  iii.,  p.  581-596),  I 
have  given  the  latitudes  of  Samarcand  and  Bokhara  according  to  the 
different  Arabic  and  Persian  MSS.  contained  in  the  Paris  Library.  I 
have  shown  that  the  former  is  probably  more  than  39°  52',  while  most 
of  the  best  manuscripts  of  Ulugh  Beg  give  39°  37',  and  the  Kitab  aL- 
athual  of  Alfares,  and  the  Kanum  of  Albyruni,  give  40°.  I  would  again 
draw  attention  to  the  importance,  in  a  geographical  no  less  than  an  as- 
tronomical point  of  view,  of  determining  the  longitude  and  latitude  of 
Samarcand  by  new  and  trustworthy  observations.  Burnes's  Travels 
have  made  us  acquainted  with  the  latitude  of  Bokhara,  as  obtained  from 
observations  of  culmination  of  stars,  which  gave  39°  43'  41".  There  is, 
therefore,  only  an  error  of  from  7  to  8  minutes  in  the  two  fine  Persian 
and  Arabic  MSS.  (Nos.  164  and  2460)  of  the  Paris  Library.  Major  Ren- 
nell,  whoso  combinations  are  generally  so  successful,  made  an  error  of 


112  COSMOS. 

and  not  visible  in  39°  52'  lat.  (?)  It  contains  only  1019 
positions  of  stars,  which  are  reduced  to  the  year  1437.  A 
subsequent  commentary  gives  300  other  stars,  observed  by 
Abu-Bekri  Altizini  in  1533.  Thus  we  pass  from  Arabs,  Per- 
sians, and  Moguls,  to  the  great  epoch  of  Copernicus,  and 
nearly  to  that  of  Tycho  Brahe. 

The  extension  of  navigation  in  the  tropical  seas,  and  in 
high  southern  latitudes,  has,  since  the  beginning  of  the  six- 
teenth century,  exerted  a  powerful  influence  on  the  gradual 
extension  of  our  knowledge  of  the  firmament,  though  in  a 
less  degree  than  that  effected  a  century  later  by  the  appli- 
cation of  the  telescope.  Both  were  the  means  of  revealing 
new  and  unknown  regions  of  space.  I  have  already,  in  other 
works,  considered*  the  reports  circulated  first  by  Americus 
Vespucius,  then  by  Magellan,  and  Pigafetta  (the  companion 
of  Magellan  and  Elcano),  concerning  the  splendor  of  the 
southern  sky,  and  the  descriptions  given  by  Vicente  Yanez 
Pinzon  and  Acosta  of  the  black  patches  (coal-sacks),  and  by 
Anghiera  and  Andrea  Corsali  of  the  Magellanic  clouds.  A 
merely  sensuous  contemplation  of  the  aspect  of  the  heavens 
here  also  preceded  measuring  astronomy.  The  richness  of 
the  firmament  near  the  southern  pole,  which,  as  is  well 
known,  is,  on  the  contrary,  peculiarly  deficient  in  stars,  was 
so  much  exaggerated  that  the  intelligent  Polyhistor  Cardanus 
indicated  in  this  region  10,000  bright  stars  which  were  said 
to  have  been  seen  by  Vespucius  with  the  naked  eye.f 

Friedrich  Houtman  and  Petrus  Theodori  of  Embden  (who, 
according  to  Olbers,  is  the  same  person  as  Dircksz  Keyser) 
now  first  appeared  as  zealous  observers.  They  measured 
distances  of  stars  at  Java  and  Sumatra ;  and  at  this  period 
the  most  southern  stars  were  first  marked  upon  the  celestial 
maps  of  Bartsch,  Hondius,  and  Bayer,  and  by  Kepler's  in- 
dustry were  inserted  in  Tycho  Brahe' s  Rudolphine  tables. 

Scarcely  half  a  century  had  elapsed  from  the  time  of  Ma- 
gellan's circumnavigation  of  the  globe  before  Tycho  com- 
menced his  admirable  observations  on  the  positions  of  the 
fixed  stars,  which  far  exceeded  in  exactness  all  that  had 
hitherto  been  done  in  practical  astronomy,  not  excepting  even 

about  19'  in  determining  the  latitude  of  Bokhara.  (Humboldt,  A  fie 
Centrale,  t.  iii.,  p.  592,  and  Sedillot,  in  the  Proligorllenes  d' Olov.g-Beg, 
p.  cxxiii.-cxxv.) 

*  Cosmos,  vol.  ii.,  p.  285-29C  ;  Humboldt,  Examen  Crit.  de  VHisloirt 
de  la  Gtogr.,  t.  iv.,  p.  321-336  :  t.  v.,  p.  226-238. 

t  Cardani  Paralipomenon,  lib.  viii.,  cap.  10.  (Opp.,  t.  ix.,  ed.  Lugd  . 
1663,  p.  508.) 


PROGRESS  OP  ASTRONOMY.          113 

the  laborious  observations  of  the  Landgrave  "William  IV.  at 
Cassel.  Tycho  Brahe's  catalogue,  as  revised  and  published 
by  Kepler,  contains  no  more  than  1000  stars,  of  which  one 
fourth  at  most  belong  to  the  sixth  magnitude.  This  cata- 
logue, and  that  of  Hevelius,  which  was  less  frequently  em- 
ployed, and  contained  1564  determinations  of  position  for  the 
year  1660,  were  the  last  which  were  made  by  the  unaided 
eye,  owing  their  compilation  in  this  manner  to  the  capricious 
disinclination  of  the  Dantzig  astronomer  to  apply  the  telescope 
to  purposes  of  measurement. 

This  combination  of  the  telescope  with  measuring  instru- 
ments— the  union  of  telescopic  vision  and  measurements — 
at  length  enabled  astronomers  to  determine  the  position  of 
stars  below  the  sixth  magnitude,  and  more  especially  between 
the  seventh  and  the  twelfth.  The  region  of  the  fixed  stars 
might  now,  for  the  first  time,  be  said  to  be  brought  within 
the  reach  of  observers.  Enumerations  of  the  fainter  tele- 
scopic stars,  and  determinations  of  their  position,  have  not 
only  yielded  the  advantage  of  making  a  larger  portion  of  the 
regions  of  space  known  to  us  by  the  extension  of  the  sphere 
of  i  •  nervation,  but  they  have  also  (what  is  still  more  import- 
ant) indirectly  exercised  an  essential  influence  on  our  knowl- 
edge of  the  structure  and  configuration  of  the  universe,  on 
tiiv.-  discovery  of  new  planets,  and  on  the  more  rapid  determ- 
ination of  their  orbits.  When  William  Herschel  conceived 
the  happy  idea  of,  as  it  were,  casting  a  sounding  line  in  the 
depths  of  space,  and  of  counting  during  his  gaugings  the  stars 
which  passed  through  the  field  of  his  great  telescope,*  at 
different  distances  from  the  Milky  Way,  the  law  was  discov- 
ered that  the  number  of  stars  increased  in  proportion  to  their 
vicinity  to  the  Milky  Way — a  law  which  gave  rise  to  the 
idea  of  the  existence  of  large  concentric  rings  filled  with 
millions  of  stars  which  constitute  the  many-cleft  Galaxy. 
The  knowledge  of  the  number  and  the  relative  position  of 
the  faintest  stars  facilitates  (as  was  proved  by  Galle's  rapid 
and  felicitous  discovery  of  Neptune,  and  by  that  of  several 
of  the  smaller  planets)  the  recognition  of  planetary  cosmic  al 
bodies  which  change  their  positions,  moving,  as  it  were,  be- 
tween fixed  boundaries.  Another  circumstance  proves  even 
more  distinctly  the  importance  of  very  complete  catalogues 
of  the  stars.  If  a  new  planet  be  once  discovered  in  the 
vault  of  heaven,  its  notification  in  an  older  catalogue  of  po- 

»  Cosmos,  vol.  i.,  p.  87-89. 


114  COSMOS. 


eitions  will  materially  facilitate  the  difficult  calculation  of 
its  orbit.  The  indication  of  a  new  star  which  has  subse- 
quently been  lost  sight  of,  frequently  affords  us  more  assist- 
ance than,  considering  the  slowness  of  its  motion,  we  can 
hope  to  gain  by  the  most  careful  measurements  of  its  course 
through  many  successive  years.  Thus  the  star  numbered  964 
in  the  catalogue  of  Tobias  Mayer  has  proved  of  great  im- 
portance for  the  determination  of  Uranus,  and  the  star  num- 
bered 26,266  in  Lalande's  catalogue*  for  that  of  Neptune 
Uranus,  before  it  was  recognized  as  a  planet,  had,  as  is  now 
well  known,  been  observed  twenty-one  times ;  once,  as  al- 
ready stated,  by  Tobias  Mayer,  seven  times  by  Flamstead, 
once  by  Bradley,  and  twelve  times  by  Le  Monnier.  It  may 
be  said  that  our  increasing  hope  of  future  discoveries  of  plan- 
etary bodies  rests  partly  on  the  perfection  of  our  telescopes 
(Hebe,  at  the  time  of  its  discovery  in  July,  1847,  was  a  star 
of  the  8-9  magnitude,  while  in  May,  1849,  it  was  only  of  the 
eleventh  magnitude),  and  partly,  and  perhaps  more,  on  the 
completeness  of  our  star  catalogues,  and  on  the  exactness 
of  our  observers. 

The  first  catalogue  of  the  stars  which  appeared  after  the 
epoch  when  Morin  and  Gascoigne  taught  us  to  combine  tele- 
scopes with  measuring  instruments,  was  that  of  the  southern 
stars  compiled  by  Halley.  It  was  the  result  of  a  short  resi- 
dence at  St.  Helena  in  the  years  1677  and  1678,  but,  singu- 
larly enough,  does  not  contain  any  determinations  below  the 
sixth  magnitude.!  Flamstead  had,  indeed,  begun  his  great 
Star  Atlas  at  an  earlier  period ;  but  the  work  of  this  cele- 
brated observer  did  not  appear  till  1712.  It  was  succeeded 
by  Bradley's  observations  (from  1750  to  1762),  which  led  to 
the  discovery  of  aberration  and  nutation,  and  have  been  ren- 
dered celebrated  by  the  Fundamenta  Astronomice  of  our 
countryman  Bessel  (1818),^  and  by  the  stellar  catalogues  of 

*  Bally,  Cat.  of  those  stars  in  the  "Histoire  Celeste"  of  Jerome  de 
Lalande,for  which  tables  of  reduction  to  the  epoch  1800  have  been  pub- 
lished by  Prof.  Schumacher,  1847,  p.  1195.  On  what  we  owe  to  the 
perfection  of  star  catalogues,  see  the  remarks  of  Sir  John  Herschel  in 
Cat.  of  the  British  Assoc.,  1845,  p.  4,  §  10.  Compare  also  on  stars  that 
have  disappeared,  Schumacher,  Astr.  Nachr.,  No.  624,  and  Bode,  Jahrb. 
fur  1817, s  249. 

t  Memoirs  of  the  Royal  Astron.  Soc.,  vol.  xiii.,  1843,  p.  33  and  168. 

t  Bessel,  Fundamenta  Astronomies  pro  anno  1755,  deducta  ex  observa- 
tionibus  viri  incomparabilis  James  Bradley  in  Specula  astronomica  Ore- 
novicensi,  1818.  Compare  also  Bessel,  Tabula  Regiomontancn  reduclio- 
num  observationum  astronomicarum  ab  anno  1750  usque  ad  annum  1850 
computatoE  (1830). 


STAR    CATALOGUES.  115 

La  Caille,  Tobias  Mayer,  Cagnoli,  Piazzi,  Zach,  Pond,  Taylor, 
Groombridge,  Argelander,  Airy,  Brisbane,  and  Riimker. 

We  here  only  allude  to  those  works  which  enumerate  a 
great  and  important  part*  of  the  stars  of  the  seventh  to  the 
tenth  magnitude  which  occupy  the  realms  of  space.  The 
catalogue  known  under  the  name  of  Jerome  de  Lalandt's, 
but  which  is,  however,  solely  based  on  observations  made  by 
his  nephew,  Francois  de  Lalande,  and  by  Burckhardt  between 
the  years  1789  and  1800,  has  only  recently  been  duly  appre- 
ciated. After  having  been  carefully  revised  by  Francis  Baily, 
under  the  direction  of  the  "  British  Association  for  the  Ad- 
vancement of  Science"  (in  1847),  it  now  contains  47,390 
stars,  many  of  which  are  of  the  ninth,  and  some  even  below 
that  magnitude.  Harding,  the  discoverer  of  Juno,  catalogued 
above  50,000  stars  in  twenty-seven  maps.  Bessel's  great 
work  on  the  exploration  of  the  celestial  zones,  which  comprises 
75,000  observations  (made  in  the  years  1825-1833  between 
— 15°  and  +45°  declination),  has  been  continued  from  1841 
to  1844  with  the  most  praiseworthy  care,  as  far  as  +80° 
decl.,  by  Argelander  at  Bonn.  Weisse  of  Cracow,  under  the 
auspices  of  the  Academy  of  St.  Petersburgh,  has  reduced 
31,895  stars  for  the  year  1825  (of  which  19,738  belonged  to 
the  ninth  magnitude)  from  Bessol's  zones,  between  — 15°  and 
+  15°  decl.  ;t  and  Argelander' s  exploration  of  the  northern 
heavens  from  +45°  to  +80°  decl.  contains  about  22,000 
well-determined  positions  of  stars. 

*  I  here  compress  into  a  note  the  numerical  data  taken  from  star  cat- 
alogues, containing  lesser  masses  and  a  smaller  number  of  positions, 
with  the  names  of  the  observers,  and  the  number  of  positions  attached : 
La  Caille,  in  scarcely  ten  months,  during  the  years  1751  and  1752,  with 
instruments  magnifying  only  eight  times,  observed  9766  southern  stars, 
to  the  seventh  magnitude  inclusive,  which  were  reduced  to  the  year 
1750  by  Henderson ;  Tobias  Mayer,  998  stars  to  1756 ;  Flamstead,  orig- 
inally only  2866,  to  which  564  were  added  by  Daily's  care  (Mem.  of  the 
Astr.  Soc.,  vol.  iv.,  p.  1291-64);  Bradley,  3222,  reduced  by  Bessel  to 
the  year  1755;  Pond,  1112;  Piazzi,,7646  to  1800;  Groombridge,  4243, 
mostly  circumpolar  stars,  to  1810  ;  Sir  Thomas  Brisbane,  and  Rflmker, 
7385  stars,  observed  in  New  Holland  in  the  years  1822-1828 ;  Airy,  2156 
stars,  reduced  to  the  year  1845 ;  Riimker,  12,000  on  the  Hamburg  hori- 
zon; Argelander  (Cat.  of  Abo),  560;  Taylor  (Madras),  11,015.  The 
British  Association  Catalogue  of  Stars  (1845),  drawn  up  under  Baily's 
superintendence,  contains  8377  stars  from  the  first  to  7i  magnitudes. 
For  the  southern  stars  we  have  the  rich  catalogues  of  Henderson,  Fal- 
lows, Maclear,  and  Johnson  at  St.  Helena. 

t  Weisse,  Positiones  media  stellarum  fixarum  in  Zonis  Regiomontanit 
a  Bessclio  inter  — 15°  ct  -J-15°  decl.  observatanim  ad  annum  1825  re 
dvcla  (1846);  with  an  important  Preface  by  Struve. 


116  COSMOS. 

I  can  not,  I  think,  make  mere  honorable  mention  of  the 
great  work  of  the  star  maps  of  the  Berlin  Academy  than  by 
quoting  the  words  used  by  Encke  in  reference  to  this  un- 
dertaking, in  his  oration  to  the  memory  of  Bessel :  ''  With 
the  completeness  of  catalogues  is  connected  the  hope  that, 
by  a  careful  comparison  of  the  different  aspects  of  the  heav- 
ens with  those  stars  which  have  been  noted  as  fixed  points, 
we  may  be  enabled  to  discover  all  moving  celestial  bodies, 
whose  change  of  position  can  scarcely,  owing  to  the  faint- 
ness  of  their  light,  be  noted  by  the  unaided  eye,  and  that 
we  may  in  this  manner  complete  our  knowledge  of  the  so- 
lar system.  While  Harding's  admirable  atlas  gives  a  per- 
fect representation  of  the  starry  heavens — as  far  as  Lalande's 
Histoire  Celeste,  on  which  it  is  founded,  was  capable  of  af- 
fording such  a  picture — Bessel,  in  1824,  after  the  comple- 
tion of  the  first  main  section  of  his  zones,  sketched  a  plan 
for  grounding  on  this  basis  a  more  special  representation  of 
the  starry  firmament,  his  object  being  not  simply  to  exhibit 
what  had  been  already  observed,  but  likewise  to  enable  as- 
tronomers, by  the  completeness  of  his  tables,  at  once  to  rec- 
ognize every  new  celestial  phenomenon.  Although  the  star 
maps  of  the  Berlin  Academy  of  Sciences,  sketched  in  ac- 
cordance with  Bessel's  plan,  may  not  have  wholly  completed 
the  first  proposed  cycle,  they  have  nevertheless  contributed 
in  a  remarkable  degree  to  the  discovery  of  new  planets,  since 
they  have  been  the  principal,  if  not  the  sole  means,  to  which, 
at  the  present  time  (1850),  we  owe  the  recognition  of  seven 
new  planetary  bodies."*  Of  the  twenty-four  maps  designed 
to  represent  that  portion  of  the  heavens  which  extends  15° 
on  either  side  of  the  equator,  our  Academy  has  already  con- 
tributed sixteen.  These  contain,  as  far  as  possible,  all  stars 
down  to  the  ninth  magnitude,  and  many  of  the  tenth. 

The  present  would  seem  a  fitting  place  to  refer  to  the 
average  estimates  which  have  been  hazarded  on  the  num- 
ber of  stars  throughout  the  whole  heavens,  visible  to  us  by 
the  aid  of  our  colossal  space-penetrating  telescopes.  Struve 
assumes  for  Herschel's  twenty-feet  reflector,  which  was  em- 
ployed in  making  the  celebrated  star-gauges  or  sweeps,  that 
a  magnifying  power  of  180  would  give  5.800,000  for  the 
number  of  stars  lying  within  the  zones  extending  30°  on  ei- 
ther side  of  the  equator,  and  20,374,000  for  the  whole  heav- 
ens. Sir  Wilh'am  Herschel  conjectured  that  eighteen  mill- 

*  Encke,  Geddchtnissrede  auf  Bessel,  s.  13. 


DISTRIBUTION    OF    THE    FIXED    STARS.  117 

ions  of  stars  in  the  Milky  Way  might  be  seen  by  his  still 
more  powerful  forty-feet  reflecting  telescope.* 

After  a  careful  consideration  of  all  the  fixed  stars,  wheth- 
er visible  to  the  naked  eye  or  merely  telescopic,  whose  po- 
sitions are  determined,  and  which  are  recorded  in  catalogues, 
we  turn  to  their  distribution  and  grouping  in  the  vault  of 
neaven. 

As  we  have  already  observed,  these  stellar  bodies,  from 
the  inconsiderable  and  exceedingly  slow  (real  and  apparent) 
change  of  position  exhibited  by  some  of  them — partly  owing 
to  precession  and  to  the  different  influences  of  the  progression 
of  our  solar  system,  and  partly  to  their  own  proper  motion — 
may  be  regarded  as  landmarks  in  the  boundless  regions  of 
space,  enabling  the  attentive  observer  to  distinguish  all  bod- 
ies that  move  among  them  with  a  greater  velocity  or  in  an 
opposite  direction — consequently,  all  which  are  allied  to  tel- 
escopic comets  and  planets.  The  first  and  predominating 
interest  excited  by  the  contemplation  of  the  heavens  is  di- 
rected to  the  fixed  stars,  owing  to  the  multiplicity  and  over- 
whelming mass  of  these  cosmical  bodies  ;  and  it  is  by  them 
that  our  highest  feelings  of  admiration  are  called  forth. 
The  orbits  of  the  planetary  bodies  appeal  rather  to  inquiring 
reason,  and,  by  presenting  to  it  complicated  problems,  tend 
to  promote  the  development  of  thought  in  relation  to  astron- 
omy. 

Amid  the  innumerable  multitude  of  great  and  small  stare, 
which  seem  scattered,  as  it  were  by  chance,  throughout  the 
vault  of  heaven,  even  the  rudest  nations  separate  single 
(and  almost  invariably  the  same)  groups,  among  which  cer- 
tain bright  stars  catch  the  observer's  eye,  either  by  their 
proximity  to  each  other,  their  juxtaposition,  or,  in  some  cases, 
by  a  kind  of  isolation.  This  fact  has  been  confirmed  by  re- 
cent and  careful  examinations  of  several  of  the  languages  of 
so-called  savage  tribes.  Such  groups  excite  a  vague  sense 
of  the  mutual  relation  of  parts,  and  have  thus  led  to  their 
receiving  names,  which,  although  varying  among  different 
races,  were  generally  derived  from  organic  terrestrial  ob- 
jects. Amid  the  forms  with  which  fancy  animated  the 
waste  and  silent  vault  of  heaven,  the  earliest  groups  thus 
distinguished  were  the  seven-starred  Pleiades,  the  seven  stars 
of  the  Great  Bear,  subsequently  (on  account  of  the  repetition 
of  the  same  form)  the  constellation  of  the  Lesser  Bear,  the 

*  Compare  Struve,  Etudes  d'Astr.  Sttllaire,  1847,  p.  66  and  72  ;  Cot- 
mo$,  vol.  i.,  p.  100;  ami  Madlec  Astr.,  4te  Aufl.,  $  417. 


118  COSMOS 

belt  of  Orion  (Jacob's  stafT),  Cassiopeia,  the  Swan,  the  Soor 
pion,  the  Southern  Cross  (owing  to  the  striking  difference 
in  its  direction  before  and  after  its  culmination),  the  South- 
ern Crown,  the  Feet  of  the  Centaur  (the  Twins,  as  it  were, 
of  the  Southern  hemisphere),  &c. 

"Wherever  steppes,  grassy  plains,  or  sandy  wastes  present 
a  far-extended  horizon,  those  constellations  whose  rising  or 
setting  corresponds  with  the  busy  seasons  and  requirements 
of  pastoral  and  agricultural  life  have  become  the  subject  of 
attentive  consideration,  and  have  gradually  led  to  a  symbol- 
izing connection  of  ideas.  Men  thus  became  familiarized 
with  the  aspect  of  the  heavens  before  the  development  of 
measuring  astronomy.  They  soon  perceived  that  besides 
the  daily  movement  from  east  to  west,  which  is  common  to 
all  celestial  bodies,  the  sun  has  a  far  slower  proper  motion  in 
an  opposite  direction.  The  stars  which  shine  in  the  even- 
ing sky  sink  lower  every  day,  until  at  length  they  are  wholly 
lost  amid  the  rays  of  the  setting  sun ;  while,  on  the  other 
hand,  those  stars  which  were  shining  in  the  morning  sky 
before  the  rising  of  the  sun,  recede  further  and  further  from 
it.  In  the  ever-changing  aspect  of  the  starry  heavens,  suc- 
cessive constellations  are  always  coming  to  view.  A  slight 
degree  of  attention  suffices  to  show  that  these  are  the  same 
which  had  before  vanished  in  the  west,  and  that  the  stars 
which  are  opposite  to  the  sun,  setting  at  its  rise,  and  rising 
at  its  setting,  had  about  half  a  year  earlier  been  seen  in  its 
vicinity.  From  the  time  of  Hesiod  to  Eudoxus,  and  from 
the  latter  to  Aratus  and  Hipparchus,  Hellenic  literature 
abounds  in  metaphoric  allusions  to  the  disappearance  of  the 
stars  amid  the  sun's  rays,  and  their  appearance  in  the  morn- 
ing twilight — their  heliacal  setting  and  rising.  An  atten- 
tive observation  of  these  phenomena  yielded  the  earliest  ele- 
ments of  chronology,  which  were  simply  expressed  in  num- 
bers, while  mythology,  in  accordance  with  the  more  cheerful 
or  gloomy  tone  of  national  character,  continued  simultane- 
ously to  rule  the  heavens  with  arbitrary  despotism. 

The  primitive  Greek  sphere  (I  here  again,  as  in  the  his- 
tory of  the  physical  contemplation  of  the  universe,*  follow 
the  investigations  of  my  intellectual  friend  Letronne)  had  be- 
come gradually  filled  with  constellations,  without  being  in 
any  degree  considered  with  relation  to  the  ecliptic.  Thus 
Homer  and  Hesiod  designate  by  name  individual  stars  and 

*   Cosmos,  vol.  ii.,  j>.  167 


ZODIACAL   SIGNS.  119 

groups ;  the  former  mentions  the  constellation  of  the  Bear 
("  otherwise  known,  as  the  Celestial  Wain,  and  which  alone 
never  sinks  into  the  bath  of  Oceanos"),  Bootes,  and  the  Dog 
of  Orion  ;  the  latter  speaks  of  Sirius  and  Arcturus,  and  both 
refer  to  the  Pleiades,  the  Hyades,  and  Orion.*  Homer's  twice 
repeated  assertion  that  the  constellation  of  the  Bear  alone 
never  sinks  into  the  ocean,  merely  allows  us  to  infer  that  in 
his  age  the  Greek  sphere  did  not  yet  comprise  the  constella- 
tions of  Draco,  Cepheus,  and  Ursa  Minor,  which  likewise  do 
not  set.  The  statement  does  not  prove  a  want  of  acquaint- 
ance with  the  existence  of  the  separate  stars  forming  these 
three  catasterisms,  but  simply  an  ignorance  of  their  arrange 
ment  into  constellations.  A  long  and  frequently  misunder- 
stood passage  of  Strabo  (lib.  i.,  p.  3,  Casaub.)  on  Homer,  II., 
xviii.,  485-489,  specially  proves  a  fact — important  to  the 
question — that  in  the  Greek  sphere  the  stars  were  only  grad- 
ually arranged  in  constellations.  Homer  has  been  unjustly 
accused  of  ignorance,  says  Strabo,  as  if  he  had  known  of  only 
one  instead  of  two  Bears.  It  is  probable  that  the  lesser  one 
had  not  yet  been  arranged  in  a  separate  group,  and  that  the 
name  did  not  reach  the  Hellenes  until  after  the  Phoanicians 
had  specially  designated  this  constellation,  and  made  use  of 
it  for  the  purposes  of  navigation.  All  the  scholia  on  Homer, 
Hyginus,  and  Diogenes  Laertius  ascribe  its  introduction  to 
Thales.  In  the  Pseudo-Eratosthenian  work  to  which  we 
have  already  referred,  the  lesser  Bear  is  called  <&otviKTj  (or, 
as  it  were,  the  Phoenician  guiding  star).  A  century  later 
(01.  71),  Cleostratus  of  Tenedos  enriched  the  sphere  with  the 
constellations  of  Sagittarius,  TO^OTT/C,  and  Aries,  K.pi6$. 

The  introduction  of  the  Zodiac  into  the  ancient  Greek 
sphere  coincides,  according  to  Letronne,  with  this  period  of 
the  domination  of  the  Pisistratidae.  Eudemus  of  Rhodes,  one 
of  the  most  distinguished  pupils  of  Aristotle,  and  author  of  a 
"History  of  Astronomy,"  ascribes  the  introduction  of  this  zo- 
diacal belt  (TI  TOV  fadiaicov  dia^dxrig,  also  £wt  Jio^  /cvwAof)  to 
(Enopides  of  Chios,  a  cotemporary  of  Anaxagoras.f  The 

*  Ideler,  Unters.  uber  die  Sternnamen,  s.  xi.,  47,  139,  144,  2 13  •  Le- 
tronne, Sur  V Origins  du  Zodiaque  Grec,  1340,  p.  25. 

t  Letronne,  op.  cit.,  p.  25 ;  and  Carteron,  Analyse  de»  Rechercn.es  de 
tl.  Letronne  sur  les  Representations  Zodiacales,  1843,  p.  119.  "It  ia 
Yery  doubtful  whether  Eudoxus  (Ol.  103)  ever  made  use  of  the  word 
Cudianof.  We  first  meet  with  it  in  Euclid,  and  in  the  Commentary  of 
Hipparchus  on  Aratus  (Ol.  160).  The  name  ecliptic,  eKfautTiicdf,  is 
also  very  recent."  Compare  Martin  in  the  Commentary  to  Thconi* 
Smyrn<ri  Plalonici  Liber  de  Aslronotnia,  1849,  p.  50,  GO. 


120  COSMOS. 

idea  of  the  relation  of  the  planets  and  fixed  stars  to  the  sun'* 
course,  the  division  of  the  ecliptic  into  twelve  equal  parts 
(Dodecatomeria),  originated  with  the  ancient  Chaldeans,  and 
very  probably  came  to  the  Greeks,  at  the  beginning  of  the 
fifth,  or  even  in  the  sixth  century  before  our  era,  direct  from 
Chaldea,  and  not  from  the  Valley  of  the  Nile.*  The  Greeks 
merely  separated  from  the  constellations  named  in  their  prim- 
itive sphere  those  which  were  nearest  to  the  ecliptic,  and 
could  be  used  as  signs  of  the  zodiac.  If  the  Greeks  had  bor- 
rowed from  another  nation  any  thing  more  than  the  idea  and 
number  of  the  divisions  (Dodecatomeria)  of  a  zodiac — if  they 
had  borrowed  the  zodiac  itself,  with  its  signs — they  would 
not  at  first  have  contented  themselves  with  only  eleven  con- 
stellations. The  Scorpion  would  not  have  been  divided  into 
two  groups  ;  nor  would  zodiacal  constellations  have  been  in- 
troduced (some  of  which,  like  Taurus,  Leo,  Pisces,  and  Virgo, 
extend  over  a  space  of  35°  to  48°,  while  others,  as  Cancer, 
Aries,  and  Capricornus,  occupy  only  from  19°  to  23°),  which 
are  inconveniently  grouped  to  the  north  and  south  of  the 
ecliptic,  either  at  great  distances  from  each  other,  or,  like  Tau- 
rus and  Aries,  Aquarius  and  Capricornus,  so  closely  crowded 
together  as  almost  to  encroach  on  each  other.  These  cir- 
cumstances prove  that  catasterisms  previously  formed  were 
converted  into  signs  of  the  zodiac. 

The  sign  of  Libra,  according  to  Letronne's  conjecture,  was 
introduced  at  the  time  of,  and  perhaps  by,  Hipparchus.  It 
is  never  mentioned  by  Eudoxus,  Archimedes,  Autolycus,  or 
even  by  Hipparchus  in  the  few  fragments  of  his  writings 
which  have  been  transmitted  to  us  (excepting  indeed  in  one 

*  Letronne,  Orig.  du  Zod.,  p.  25 ;  and  Analyse  Crit.  des  Reprtt. 
Zod.,  1846,  p.  15.  Ideler  and  Lepsius  also  consider  it  probable  "  that 
the  knowledge  of  the  Chaldean  zodiac,  as  well  in  reference  to  its  divi- 
sions as  to  the  names  of  the  latter,  had  reached  the  Greeks  in  the  sev- 
enth century  before  our  era,  although  the  adoption  of  the  separate  signs 
of  the  zodiac  in  Greek  astronomical  literature  was  gradual  and  of  a  sub- 
sequent d*te."  (Lepsius,  Chronologic  der  ^Egypter,  1849,  s.  65  and 
124.)  Ideler  is  inclined  to  believe  that  the  Orientals  had  names,  but 
not  constellations  for  the  Dodecatomeria,  and  Lepsius  regards  it  as  a 
natural  assumption  "  that  the  Greeks,  at  the  period  when  their  sphere 
was  for  the  most  part  unfilled,  should  have  added  to  their  own  the 
Chaldean  constellations,  from  which  the  twelve  divisions  were  named." 
But  are  we  not  led  on  this  supposition  to  inquire  why  the  Greeks  had 
at  first  only  eleven  signs  instead  of  introducing  all  the  twelve  belong- 
ing to  the  Chaldean  Dodecatomeria  ?  If  they  introduced  the  twelve 
signs,  they  are  hardly  likely  to  hava  removed  one  in  order  to  replace  it 
at  a  subseq  :en*  period. 


ZODIACAL    SIGNS.  121 

passage,  probably  falsified  by  a  copyist).*  The  earliest  no- 
tice of  this  new  constellation  occurs  in  Geminus  and  Varro 
scarcely  half  a  century  before  our  era  ;  and  as  the  Romans, 
from  the  time  of  Augustus  to  Antoninus,  became  more  strong- 
ly imbued  with  a  predilection  for  astrological  inquiry,  those 
constellations  which  "  lay  in  the  celestial  path  of  the  sun" 
acquired  an  exaggerated  and  fanciful  importance  The  Egyp- 
tian zodiacal  constellations  found  at  Dendera,  Esneh,  the 
Propylon  of  Panopolis,  and  on  some  mummy-cases,  belong  to 
the  first  half  of  this  period  of  the  Roman  dominion,  as  was 
maintained  by  Visconti  and  Testa,  at  a  time  when  the  nec- 
essary materials  for  the  decision  of  the  question  had  not  been 
collected,  and  the  wildest  hypothesis  still  prevailed  regard- 
ing the  signification  of  these  symbolical  zodiacal  signs,  and 
their  dependence  on  the  precession  of  the  equinoxes.  The 
great  antiquity  which,  from  passages  in  Manu's  Book  of 
Laws,  Valmiki's  Ramayana  and  Amarasinha's  Dictionary, 
Augustus  "William  von  Schlegel  attributed  to  the  zodiacal 
circles  found  in  India,  has  been  rendered  very  doubtful  by 
Adolph  Holtzmann's  ingenious  investigations.! 

*  On  the  passage  referred  to  in  the  text,  and  interpolated  by  a  copy 
ist  of  Hipparchus,  see  Letronne,  Orie.  du  Zod.,  1840,  p.  20.  As  early 
as  1812,  when  I  was  much  disposed  to  believe  that  the  Greeks  had 
been  long  acquainted  with  the  sign  of  Libra,  I  directed  attention  in  an 
elaborate  memoir  (on  all  the  passages  in  Greek  and  Roman  writers  of 
antiquity,  in  which  the  Balance  occurs  as  a  sign  of  the  zodiac)  to  that 
passage  in  Hipparchus  (Comment,  in  Aratum,  lib.  iii.,  cap.  2)  which  re- 
fers to  the  tiripiov  held  by  the  Centaur  (in  his  fore-foot),  as  well  as  to 
the  remarkable  passage  of  Ptolemy,  lib.  ix.,  cap.  7  (Halma,  t.  ii.,  p. 
170).  In  the  latter  the  Southern  Balance  is  named  with  the  affix  KOTO 


f  ,  and  is  opposed  to  the  pincers  of  the  Scorpion  in  an  observ- 
ation, which  was  undoubtedly  not  made  at  Babylon,  but  by  some  of 
the  astrological  Chaldeans,  dispersed  throughout  Syria  and  Alexandria. 
(  Vues  des  Cordilleret  et  Monument  des  Peuples  Indigenes  de  I'Amerique, 
t.  ii.,  p.  380.)  Buttman  maintained,  what  is  very  improbable,  that  the 
£7/A<u  originally  signi6ed  the  two  scales  of  the  Balance,  and  were  sub- 
sequently by  some  misconception  converted  into  the  pincers  of  a  scor- 
pion. (Compare  Ideler,  Untersuchungen  uber  die  astronomischen  Beo- 
bachtungen  der  Alien.,  8.  374,  and  Ueber  die  Sternnamen,  s.  174-177, 
with  Carteron,  Recherches  de  M.  Letronne,  p.  113.)  It  is  a  remarkable 
circumstance  connected  with  the  analogy  between  many  of  the  names 
of  the  twenty-seven  "  houses  of  the  moon,"  and  the  Dodecatomeria  of 
the  zodiac,  that  we  also  meet  with  the  sign  of  the  Balance  among  the 
Indian  Nakschatras  (Moon-houses),  which  are  undoubtedly  of  very 
great  antiquity.  (  Vites  des  Cordilleres,  t.  ii.,  p.  6-12.) 

t  Compare  A.  W.  von  Schlegel,  Ueber  Sternbilder  des  Thierkreises  im 
alien  Indien,  in  the  Zeitschrift  fur  die  Kunde  det  Morgenlandes,  bd.  i., 
Heft  3,  1837,  and  his  Commentatio  de  Zodiari  Antiquitate  et  Origins, 
1839,  with  Adolph  Holtzmaun,  Ueber  den  Griechtichen  Ursprung  det  In 

Vo*.  III.—  F 


122  COSMOS. 

The  artifical  grouping  of  the  stars  into  constellations, 
which  arose  incidentally  during  the  lapse  of  ages — the  fre- 
quently inconvenient  extent  and  indefinite  outline — the  com- 
plicated designations  of  individual  stars  in  the  different  con- 
stellations— the  various  alphabets  which  have  been  required 
to  distinguish  them,  as  in  Argo — together  with  the  tasteless 
blending  of  mythical  personages  with  the  sober  prose  of  philo- 
sophical instruments,  chemical  furnaces,  and  pendulum  clocks, 
in  the  southern  hemisphere,  have  led  to  many  propositions 
for  mapping  the  heavens  in  new  divisions,  without  the  aid 
of  imaginary  figures.  This  undertaking  appears  least  haz- 
ardous in  respect  to  the  southern  hemisphere,  where  Scorpio, 
Sagittarius,  Centaurus,  Argo,  and  Eridanus  alone  possess  any 
poetic  interest.* 

The  heavens  of  the  fixed  stars  (orbis  inerrans  of  Apule- 
ius),  and  the  inappropriate  expression  of  fixed  stars  (astro, 
fixa  of  Manilius),  reminds  us,  as  we  have  already  observed 
in  the  introduction  to  the  Astrognosy,f  of  the  connection,  or, 
rather,  confusion  of  the  ideas  of  insertion,  and  of  absolute  im- 
mobility or  fixity.  When  Aristotle  calls  the  non-wandering 
celestial  bodies  (dnXavrj  darpa)  riveted  (ivdede^iva),  when 
Ptolemy  designates  them  as  ingrafted  (TrpoanefivKorec;),  these 
terms  refer  specially  to  the  idea  entertained  by  Anaximenes 
of  the  crystalline  sphere  of  heaven.  The  apparent  motion 
of  all  the  fixed  stars  from  east  to  west,  while  their  relative 
distances  remained  unchanged,  had  given  rise  to  this  hypoth- 
esis. "  The  fixed  stars  (drrAavr/  aarpa)  belong  to  the  higher 
and  more  distant  regions,  in  which  they  are  riveted,  like  nails, 

dischcn  Thierkreises,  1841,  s.  9,  16,  23.  "  The  passages  quoted  from 
Amorakoscha  and  Ramayana,"  says  the  latter  writer,  "admit  of  un- 
doubted interpretation,  and  speak  of  the  zodiac  in  the  clearest  terms ; 
but  if  these  works  were  composed  before  the  knowledge  of  the  Greek 
signs  of  the  zodiac  could  have  reached  India,  these  passages  ought  to 
be  carefully  examined  for  the  purpose  of  ascertaining  whether  they 
may  not  be  comparatively  modern  interpolations." 

*  Compare  Buttman,  in  Berlin  Astron.  Jahrbuchfur  1822,  s.  93,  Ol- 
bers  on  the  more  recent  constellations  in  Schumacher's  Jahrbuch  fur 
1840,  s.  283-251,  and  Sir  John  Herschel,  Revision  and  Rearrangement 
of  the  Constellations,  with  special  reference  to  those^  of  the  Southern  Hem- 
uphere,  in  the  Memoirs  of  the  Astr.  Soc.,  vol.  xii.,  p.  201-224  (with  a 
very  exact  distribution  of  the  southern  stars  from  the  first  to  the  fourth 
magnitude).  On  the  occasion  of  Lalande's  formal  discussion  with  Bode 
on  the  introduction  of  his  domestic  cat  and  of  a  reaper  (Messier!),  Ol- 
bers  complains  that  in  order  "  to  find  space  in  the  firmament  for  Kirg 
Frederic's  glory,  Andromeda  must  lay  her  right  arm  in  a  different  place 
from  that  which  it  had  occupied  for  3000  years !" 

t  Vide  supra,  p.  26-28,  and  note. 


THE  FIXED  STARS.  123 


to  the  crystalline  heavens  ;  the  planets  (aarpa 
or  TrAavT/rd),  which  move  in  an  opposite  direction,  belong  to 
a  lower  and  nearer  region."*  As  we  find  in  Manilius,  in 
the  earliest  ages  of  the  Caesars,  that  the  term  Stella  fixa  was 
substituted  for  infixa  or  affiza,  it  may  be  assumed  that  the 
schools  of  Rome  attached  thereto  at  first  only  the  original 
signification  of  riveted  ;  but  as  the  word  Jixus  also  embraced 
the  idea  of  immobility,  and  might  even  be  regarded  as  sy- 
nonymous with  immotus  and  immobilis,  we  may  readily  con- 
ceive that  the  national  opinion,  or,  rather,  usage  of  speech, 
should  gradually  have  associated  with  Stella  fixa  the  idea  of 
immobility,  without  reference  to  the  fixed  sphere  to  which  it 
was  attached.  In.  this  sense  Seneca  might  term  the  world 
of  the  fixed  stars  fixum  et  immobilem  populum. 

Although,  according  to  Stobseus,  and  the  collector  of  the 
"  Views  of  the  Philosophers,"  the  designation  "  crystal  vault 
of  heaven"  dates  as  far  back  as  the  early  period  of  Anax- 
imenes,  the  first  clearly-defined  signification  of  the  idea  on 
which  the  term  is  based  occurs  in  Empedocles.  This  phi- 
losopher regarded  the  heaven  of  the  fixed  stars  as  a  solid 
mass,  formed  from  the  ether  which  had  been  rendered  crys- 
talline and  rigid  by  the  action  of  fire.f  According  to  his 

*  According  to  Democritus  and  his  disciple  Metrodorus,  Stob.,  Eclog. 
Phys.,  p.  582. 

t  Plut.,  De  plac.  Phil.,  ii.,  11;  Diog.  Laert.,  viii.,  77;  Achilles  Tat., 
ad.  Arat.,  cap.  5,  EMTT,  Kpvara^un  TOVTOV  (TOV  ovpavbv)  elvai  (fujaiv,  ix 
TOV  KayeTudovc.  ffv/.AeyevTO  ;  in  like  manner,  we  only  meet  with  the 
expression  crystal-likti  in  Diog.  Laert.,  viii.,  77,  and  Galenus,  Hist.  Phil., 
I'-i  (Sturz,  Empedocles  Agrigent.,  t.  i.,  p.  321).  Lactautius,  De  Opificio 
Dei,  c.  17  :  "  An,  si  milii  quispiam  dixerit  tcncum  esse  ccelum,  aut  vi- 
treum,  aut,  ut  Empedocles  ait,  aCrem  glacialum,  statimne  assentiat  quia 
cajliim  ex  qua  materia  sit,  ignorem."  "  If  any  one  were  to  tell  me  that 
the  heavens  are  made  of  brass,  or  of  glass,  or,  as  Empedocles  asserts, 
of  frozen  air,  I  should  incontinently  assent  thereto,  for  I  am  ignorant  of 
what  substance  the  heavens  are  composed."  We  have  no  early  Hel- 
lenic testimony  of  the  use  of  this  expression  of  a  glass-like  or  vitreous 
heaven  (cesium  vitreum'),  for  only  one  celestial  body,  the  sun,  is  called 
by  PhilolaUs  a  glass-like  body,  which  throws  upon  us  the  rays  it  has 
received  from  the  central  fire.  (The  view  of  Empedocles,  referred 
to  in  the  text,  of  the  reflection  of  the  sun's  light  from  the  body  of  the 
moon  (supposed  to  be  consolidated  in  the  same  manner  as  hailstones), 
is  frequently  noticed  by  Plutarch,  apud  Euseb.  Prtep.  Evangel.,  1,  p. 
24,  D,  and  De  Facie  in  Orbe  Lunte,  cap.  5.)  Where  Uranos  is  described 
as  xaZiceof  and  otdrjpeof  by  Homer  and  Pindar,  the  expression  refers 
only  to  the  idea  of  steadfast,  permanent,  and  imperishable,  as  in  speak- 
ing of  brazen  hearts  and  brazen  voices.  V61cker  uber  Homerische  Geo- 
graphie,  1830.  s.  5.  The  earliest  mention,  before  Pliny,  of  the  word 
Kov<Tra/lAof  when  applied  to  ice-like,  transparent  rock-crystal,  occurs  in 
Uionysius  Periegetes,  781,  Lilian,  xv.,  8,  and  Strabo,  xv.,  p.  717  Ca- 


124  COSMOS. 

theory,  the  moon  is  a  body  conglomerated  (like  hail)  by  the 
action  of  fire,  and  receives  its  light  from  the  sun.  The  original 

saub.  The  opinion  that  the  idea  of  the  crystalline  heavens  being  a  gla- 
cial vault  (atr  glacintvs  of  Lactantius)  arose  among  the  ancients,  from 
their  knowledge  of  the  decrease  of  temperature,  with  the  increase  of 
height  in  the  strata  of  the  atmosphere,  as  ascertained  from  ascending 
great  heights  and  from  the  aspect  of  snow-covered  mountains,  is  refuted 
by  the  circumstance  that  they  regarded  the  fiery  ether  as  lying  beyond 
the  confines  of  the  actual  atmosphere,  and  the  stars  as  warm  bodies. 
(Aristot.,  Meteor.,  1,3;  De  Casio,  11,  7,  p.  289.)  In  speaking  of  the 
music  of  the  spheres  (Aristot.,  De  Casio,  11,  p.  290),  which,  according 
to  the  views  of  the  Pythagoreans,  is  not  perceived  by  men,  because  it 
is  continuous,  whereas  tones  can  only  be  heard  when  they  are  inter- 
rupted by  silence,  Aristotle  singularly  enough  maintains  that  the  move- 
ment of  the  spheres  generates  heat  in  the  air  below  them,  while  they 
are  themselves  not  heated.  Their  vibrations  produce  heat,  but  no  sound. 
"  The  motion  of  the  sphere  of  the  fixed  stars  is  the  most  rapid  (Aristot., 
De  Caelo,  ii.,  10,  p.  291)  ;  as  ths  sphere  and  the  bodies  attached  to  it  are 
impelled  in  a  circle,  the  subjacent  space  is  heated  by  this  movement, 
aud  hence  heat  is  diffused  to  the  surface  of  the  earth."  (Meteorol.,  1,  3, 
p.  340.)  It  has  always  struck  me  as  a  circumstance  worthy  of  remark, 
that  the  Stagirite  should  constantly  avoid  the  word  crystal  heaven;  for 
the  expression,  "  riveted  stars"  (kv6ede[ieva  aarpa),  which  he  uses,  in- 
dicates a  general  idea  of  solid  spheres,  without,  however,  specifying  the 
nature  of  the  substance.  We  do  riot  meet  with  any  allusion  to  the  sub- 
ject in  Cicero,  but  we  find  in  his  commentator,  Macrobius  (Cic.  Som- 
nium  Scipionis,  1,  c.  20,  p.  99,  ed.  Bip.),  traces  of  freer  ideas  on  the  dim- 
inution of  temperature  with  the  increase  of  height.  According  to  him, 
eternal  cold  prevails  in  the  outermost  zones  of  heaven.  "  Ita  enim  not 
solum  ten-am  sed  ipsum  quoque  coelum,  quod  vere  mundus  vocatur, 
temperari  a  sole  certissimum  est,  ut  extremitates  ejus,  quae  via  solis 
longissime  recesserunt,  omni  careant  beneficio  caloris,  et  una  frigoris 
perpetuitate  torpescant."  "  For  as  it  is  most  certain  that  not  only  the 
earth,  but  the  heavens  themselves,  which  are  truly  called  the  universe, 
are  rendered  more  temperate  by  the  sun,  so  also  their  confines,  which 
are  most  distant  from  the  sun,  are  deprived  of  the  benefits  of  heat,  and 
languish  in  a  state  of  perjpetual  cold."  These  confines  of  heaven  (ex- 
tremitates cceli),  in  which  the  Bishop  of  Hippo  (Augustinus,  ed.  Antv., 
1700,  i.,  p.  102,  and  iii.,  p.  99)  placed  a  region  of  icy-cold  water  near 
Saturn  the  highest,  and  therefore  the  coldest,  of  all  the  planets,  are 
within  the  actual  atmosphere,  for  beyond  the  outer  limits  of  this  space 
lies,  according  to  a  somewhat  earlier  expression  of  Macrobius  (1,  c.  19, 
p.  93),  the  fiery  ether  which  enigmatically  enough  does  not  prevent  this 
eternal  cold:  "  Stellte  supra  coalum  locate,  in  ipso  purissimo  asthere  suut, 
in  quo  omne  quidquid  est,  lux  naturalis  et  sua  est,  quae  tota  cum  igne 
suo  its  sphasrae  solis  incumbit,  ut  cceli  zonas,  quas  procul  a  sole  suut, 
perpetno  frigore  oppressae  sint."  "  The  stars  above  the  heavens  are 
situated  in  the  pure  ether,  in  which  all  things,  whatever  they  may  be, 
have  a  natural  and  proper  light  of  their  own"  (the  region  of  self-lumin- 
ous stars),  "  which  so  impends  over  the  sphere  of  the  sun  with  all  its 
fire,  that  those  zones  of  heaven  which  are  far  from  the  sun  are  oppress- 
ed by  perpetual  cold."  My  reason  for  entering  so  circumstantially  into 
the  physical  and  meteorological  ideas  of  the  Greeks  and  Romans  is  sim- 
ply because  these  subjects,  except  in  the  works  of  Ukert,  Henri  Martin, 


THB  FIXED  STARS.  125 

idea  of  transparency,  congelation,  and  solidity  would  not,  ac- 
cording to  the  physics  of  the  ancients,*  and  their  ideas  of  the 
solidification  of  fluids,  have  referred  directly  to  cold  and  ice  : 
but  the  affinity  between  jcpvaroAAof,  fpuoc,  and  *pwrr<uv&>. 
as  well  as  this  comparison  with  the  most  transparent  of  all 
bodies,  gave  rise  to  the  more  definite  assertion  that  the  vault 
of  heaven  consisted  of  ice  or  of  glass.  Thus  we  read  in  Lac- 
tantius :  "  Ccelum  aerem  glaciatum  esse"  and  "  vitreum  coe- 
lum."  Empedocles  undoubtedly  did  not  refer  to  the  glass  of 
the  Phoenicians,  but  to  air,  which  was  supposed  to  be  con- 
densed into  a  transparent  solid  body  by  the  action  of  the  fiery 
ether.  In  this  comparison  with  ice  (cpvoTaAAof),  the  idea 
of  transparency  predominated ;  no  reference  being  here  made 
to  the  origin  of  ice  through  cold,  but  simply  to  its  conditions 
of  transparent  condensation.  "While  poets  used  the  term 
crystal,  prose  writers  (as  found  in  the  note  on  the  passage 
cited  from  Achilles  Tatius,  the  commentator  of  Aratus)  lim- 
ited themselves  to  the  expression  crystalline  or  crystal-like, 
Kpvo-a/J.o£i6fi$.  In  like  manner,  Trayoc  (from  tr^ywaBfu, 
to  become  solid)  signifies  a  piece  of  ice — its  condensation  be 
ing  the  sole  point  referred  to. 

The  idea  of  a  crystalline  vault  of  heaven  was  handed 
down  to  the  Middle  Ages  by  the  fathers  of  the  Church,  who* 
believed  the  firmament  to  consist  of  from  seven  to  ten  glassy 
strata,  incasing  one  another  like  the  different  coatings  of  an 
onion.  This  supposition  still  keeps  its  ground  in  some  of  the 
monasteries  of  Southern  Europe,  where  I  was  greatly  sur- 
prised to  hear  a  venerable  prelate  express  an  opinion  in  ref- 
erence to  the  fall  of  aerolites  at  Aigle,  which  at  that  time 
formed  a  subject  of  considerable  interest,  that  the  bodies  we 
called  meteoric  stones  with  vitrified  crusts  were  not  portions 
of  the  fallen  stone  itself,  but  simply  fragments  of  the  crys- 

and  the  admirable  fragment  of  the  Meteorologia  Vetenm  of  Julias  Ide- 
ler.  have  hitherto  been  very  imperfectly,  and,  for  the  most  part,  super 
ficially  considered. 

*  The  ideas  that  fire  has  the  power  of  making  rigid  (Aristot.,  ProbL, 
xiv..  11).  and  that  the  formation  of  ice  itself  may  be  promoted  by  beat, 
are  deeply  rooted  in  the  physics  of  the  ancients,  and  based  on  a  fanci- 
ful theory  of  contraries  (AnJiperittatit) — on  obscure  conceptions  of  po- 
larity (of  exciting  opposite  qualities  or  conditions).  (  Vide  mpra,  p. 
14,  and  note.)  The  quantity  of  hail  produced  was  considered  to  be 
proportional  to  the  degree  of  heat  of  the  atmospheric  strata.  (Aristot., 
Meteor.,  i..  12.)  In  the  winter  fishery  on  the  shores  of  the  Euxin-s 
warm  water  was  used  to  increase  the  ice  formed  in  the  neighborhood 
of  an  upright  tube.  (Alex.  Aphrodu.,  foL  86,  and  Plat,  De\ 
do,  c.  12.) 


126  COSMOS. 

tal  vault  shattered  by  it  in  its  fall.  Kepler,  from  his  con- 
siderations of  comets  which  intersect  the  orbits  of  all  the 
planets,*  boasted,  nearly  two  hundred  and  fifty  years  ago, 
that  he  had  destroyed  the  seventy-seven  concentric  spheres 
of  the  celebrated  Girolamo  Fracastoro,  as  well  as  all  tki? 
more  ancient  retrograde  epicycles.  The  ideas  entertained 
by  such  great  thinkers  as  Eudoxus,  Mensechmus,  Aristotle, 
and  Apollonius  Pergaeus,  respecting  the  possible  mechanism 
and  motion  of  these  solid,  mutually  intersecting  spheres  by 
which  the  planets  were  moved,  and  the  question  whether 
they  regarded  these  systems  of  rings  as  mere  ideal  modes  of 
representation,  or  intellectual  fancies,  by  means  of  which  diffi- 
cult problems  of  the  planetary  orbits  might  be  solved  or  de- 
termined approximately,  are  subjects  of  which  I  have  already 
treated  in  another  place,t  and  which  are  not  devoid  of  interest 
in  our  endeavors  to  distinguish  the  different  periods  of  devel- 
opment which  have  characterized  the  history  of  astronomy. 
Before  we  pass  from  the  very  ancient,  but  artificial  zodi- 
acal grouping  of  the  fixed  stars,  as  regards  their  supposed 
insertion  into  solid  spheres,  to  their  natural  and  actual  ar- 
rangement, and  to  the  known  laws  of  their  relative  distri- 
bution, it  will  be  necessary  more  fully  to  consider  some  of 
the  sensuous  phenomena  of  the  individual  cosmical  bodies — 
their  extending  rays,  their  apparent,  spurious  disk,  and  their 
differences  of  color.  In  the  note  referring  to  the  invisibility 
of  Jupiter's  satellites,^:  I  have  already  spoken  of  the  influ- 
ence of  the  so-called  tails  of  the  stars,  which  vary  in  num- 
ber, position,  and  length  in  different  individuals.  Indistinct- 
ness of  vision  (la  vue  indistincte)  arises  from  numerous  or- 
ganic causes,  depending  on  aberration  of  the  sphericity  of 

*  Kepler  expressly  says,  in  his  Stella  Mortis,  fol.  9 :  "  Solidos  orbes 
rejeci."  "I  have  rejected  the  idea  of  solid  orbs;"  and  in  the  Stella 
Nova,  1606,  cap.  2,  p.  8:  "  Planetse  in  puro  aethere,  perinde  atque 
aves  in  aftre  cursus  suos  conficiunt."  "  The  planets  perform  their 
course  in  the  pure  ether  as  birds  pass  through  the  air."  Compare  also 
p.  122.  He  inclined,  however,  at  an  earlier  period,  to  the  idea  of  a 
solid  icy  vault  of  heaven  congealed  from  the  absence  of  solar  heat : 
"  Orbis  ex.  aqua  factus  gelu  concreta  propter  solis  absentiam."  (Kepler, 
Epit.  Astr.  Copern.,  i.,  2,  p.  51.)  "  Two  thousand  years  before  Kepler, 
Empedocles  maintained  that  the  fixed  stars  were  riveted  to  the  crystal 
heavens,  but  that  the  planets  were  free  and  unrestrained"  (roif  Se  Trhav- 
•firae  avtiadai).  (Plut.,  plac.  Phil.,  ii.,  13;  Eraped.,  1,  p.  335,  Sturz; 
Euseb.,  Preep.  Evang.,  xv.,  30,  col.  1688,  p.  839.)  It  is  difficult  to  con- 
ceive how,  according  to  Plato  in  the  Titnueus  (  Tim.,  p.  40,  B  ;  see  Bohn's 
edition  of  Plato,  vol.  ii.,  p.  344;  but  not  according  to  Aristotle),  the  fixed 
stars,  riveted  as  they  are  to  solid  spheres,  could  rotate  independently. 

t  Cosmos,  vol.  ii.,  p   315,  316.  t  Vide  supra,  p.  51,  and  note. 


VELOCITY    OF   LIGHT. 

tne  eye,  diffraction  at  the  margins  of  the  pupil,  or  at  the 
eyelashes,  and  on  the  more  or  less  widely-diffused  irritabili- 
ty of  the  retina  from  the  excited  point.*  I  see  very  regu- 

*  "Le3  principales  causes  de  la  vue  iudistincte  sont:  aberration  de 
sphericite  de  1'oeil,  diffraction  sur  les  bords  de  la  pupille,  communica- 
tion d'irritabilite  4  des  points  voisius  sur  la  retine.  La  vue  confuse  est 
celle  ou  le  foyer  ne  tombe  pas  exactement  sur  la  retine,  mais  tombe 
au-clevant  ou  derriere  la  retine.  Les  queues  des  etoiles  sont  1'effet  de 
la  vision  iudistincte,  autant  qu'elle  depend  de  la  constitution  du  cristal- 
lin.  D'apres  un  tres  ancien  m^moire  de  Hassenfratz  (1809)  '  les  queues 
au  nombre  de  4  ou  8  qu'offrent  les  etoiles  ou  une  bougie  vue  4  25  me- 
tres de  distance,  sont  les  caustiques  du  cristallin  formees  par  1'interseo 
tiou  des  rayons  refractes.'  Ces  caustiques  se  meuvent  a  mesure  que 
nous  iuclinons  la  tete.  La  propriete  de  la  lunette  de  terminer  1'image 
lait  qu'elle  concentre  dans  un  petit  espace  la  lumiere  qui  sans  cela  en 
aurait  occupe  uu  plus  grand.  Cela  est  vrai  pour  les  etoiles  fixes  el 
pour  les  disques  des  planetes.  La  lumiere  des  etoiles  qui  n'ont  pas  de 
disque  reels,  conserve  la  me  me  intensite,  quel  que  soil  le  grossissement. 
Le  foud  de  1'air  duquel  se  detache  1'etoile  dans  la  lunette,  devient  plus 
noir  par  le  grossisseraent  qui  dilate  les  molecules  de  1'air  qu'embrasse 
le  champ  de  la  lunette.  Les  planetes  a  vrais  disques  deviennent  elles- 
m^mes  plus  pales  par  cet  effet  de  dilatation.  Quand  la  peinture  focale 
est  uette,  quand  les  rayons  partis  <fun  point  de  1'objet  se  sont  concen- 
tr6s  en  un  seul  point  dans  1'image,  1'oculaire  donne  des  resultats  satis- 
faisants.  Si  au  contraire  les  rayons  emanes  d'un  point  ne  se  reiinissent 
pas  au  foyer  en  un  seul  point,  s'ils  y  forment  un  petit  cercle,  les  images 
de  deux  points  contigus  de  1'objet  empietent  necessairement  1'une  sur 
1'autre;  leurs  rayons  se  confondeut.  Cette  confusion  la  lentille  ocu- 
laire  ue  saurait  la  faire  disparaitre.  L'office  qu'elle  remplit  exclusive- 
ment,  c'est  de  grossir ;  elle  grossit  tout  ce  qui  est  dans  1'image,  les  de- 
fauts  comme  le  reste.  Les  etoiles  n'ayant  pas  de  diametres  angulaires 
sensibles,  ceux  qu'elles  conservent  toujours,  tiennent  pour  la  plus  grande 
partie  au  manque  de  perfection  des  instrumens  (£.  la  courbure  moins 
reguliere  donnee  aux  deux  faces  de  la  lentille  objective)  et  &  quelques 
defauts  et  aberrations  de  notre  ceil.  Plus  une  6toile  semble  petite, 
tout  etant  egal  quant  au  diametre  de  1'objectif,  au  grossiasement  em- 
ploy6  et  A  1'eclat  de  Petoile  observee,  et  plus  la  lunette  a  de  perfection. 
Or  le  meilleur  moyen  de  juger  si  les  etoiles  sont  tres  petites,  si  des 
points  sont  representes  au  foyer  par  des  simples  points,  c'est  evidem- 
ment  de  viser  ^.  des  etoiles  excessivement  rapproch6es  entr'elles  et  de 
voir  si  dans  les  etoiles  doubles  connues  les  images  se  confondent,  si 
elles  empietent  1'une  sur  1'autre,  ou  bien  si  on  les  apercoit  bien  nette- 
ment  separees." 

"  The  pi-incipal  causes  of  indistinct  vision  are,  aberration  of  the  sphe- 
ricity of  the  eye,  diffraction  at  the  margins  of  the  pupil,  and  irritation 
transmitted  to  contiguous  points  of  the  retina.  Indistinct  vision  exists 
where  the  focus  does  not  fall  exactly  ou  the  retina,  but  either  somewhat 
before  or  behind  it.  The  tails  of  the  stars  are  the  result  of  indistinct- 
ness of  vision,  as  far  as  it  depends  on  the  constitution  of  the  crystalline 
lens.  According  to  a  very  old  paper  of  Hassenfratz  (1809),  '  the  four 
or  eight  tails  which  surround  the  stars  or  a  candle  seen  at  a  distance 
of  25  metres  [82  feet],  are  the  caustics  formed  on  the  crystalline  lens 
by  the  intersection  ofrefracted  rays.'  These  caustics  follow  the  move* 


128  COSMOS. 

laxly  eight  rays  at  angles  of  45°  in  stars  from  the  first  to  the 
third  magnitude.  As,  according  to  Hassenfratz,  these  radi- 
ations are  caustics  intersecting  one  another  on  the  crystal- 
line lens,  they  necessarily  move  according  to  the  direction 
in  which  the  head  is  inclined.*  Some  of  my  astronomical 
friends  see  three,  or,  at  most,  four  rays  ahove,  and  none  be- 
IOAV  the  star.  It  has  always  appeared  extraordinary  to  me 
that  the  ancient  Egyptians  should  invariably  have  given 
only  five  rays  to  the  stars  (at  distances,  therefore,  of  72°) ; 
so  that  a  star  in  hieroglyphics  signifies,  according  to  Hora- 
pollo,  the  number  five.f 

The  rays  of  the  stars  disappear  when  the  image  of  the 
radiating  star  is  seen  through  a  very  small  aperture  made 

ments  of  the  head.  The  property  of  the  telescope,  in  giving  a  definite 
outline  to  images,  causes  it  to  concentrate  in  a  small  space  the  light 
which  would  otherwise  be  more  widely  diffused.  This  obtains  for  the 
fixed  stars  and  for  the  disks  of  planets.  The  light  of  stars  having  no 
actual  disks,  maintains  the  same  intensity,  whatever  may  be  the  mag- 
nifying power  of  the  instrument.  The  aerial  field  from  which  the  star 
is  projected  in  the  telescope  is  rendered  more  black  by  the  magnifying 
property  of  the  instrument,  by  which  the  molecules  of  air  included  in 
the  field  of  view  are  expanded.  Planets  having  actual  disks  become 
fainter  from  this  effect  of  expansion.  When  the  focal  image  is  clearly 
defined,  and  when  the  rays  emanating  from  one  point  of  the  object  are 
concentrated  into  one  point  in  the  image,  the  ocular  focus  affords  satis- 
factory results.  But  if,  on  the  contrary,  the  rays  emanating  from  one 
point  do  not  reunite  in  the  focus  into  one  point,  but  form  a  small  circle, 
the  images  of  two  contiguous  points  of  the  object  will  necessarily  im- 
pinge upon  each  other,  and  their  rays  will  be  confused.  This  confusion 
can  not  be  removed  by  the  ocular,  since  the  only  part  it  performs  is 
that  of  magnifying.  It  magnifies  every  thing  comprised  in  the  image, 
including  its  defects.  As  the  stars  have  no  sensible  angular  diameters, 
those  which  they  present  are  principally  owing  to  the  imperfect  con- 
struction of  the  instrument  (to  the  different  curvatures  of  the  two  sides 
of  the  object-glass),  and  to  certain  defects  and  aberrations  pertaining 
to  the  eye  itself.  The  smaller  the  star  appears,  the  more  perfect  is  the 
instrument,  providing  all  relations  are  equal  as  to  the  diameter  of  the 
object-glass,  the  magnifying  power  employed,  and  the  brightness  of  the 
star.  Now  the  best  means  of  judging  whether  the  stars  are  very  small, 
and  whether  the  points  are  represented  in  the  focus  by  simple  points, 
is  undoubtedly  that  of  directing  the  instrument  to  stars  situated  very 
near  each  other,  and  of  observing  whether  the  images  of  known  double 
stars  are  confused,  and  impinging  on  each  other,  or  whether  they  can 
be  seen  separate  and  distinct."  (Arago,  MS.  of  1834  and  1847.) 

*  Hassenfratz,  Sur  les  rayons  divergens  des  Etoiles  in  Delam6therie, 
Journal  de  Physique,  torn.  Ixix.,  1809,  p.  324. 

t  Horapollinis  Niloi  Hieroglyphica,  ed.  Con.  Leemans,  1835,  cap.  13, 
p.  20.  The  learned  editor  notices,  however,  in  refutation  of  Jomard's 
assertion  (Descr.  de  VEgypte,  torn,  vii.,  p.  423),  that  a  star,  as  the  nu- 
merical hieroglyphic  for  5,  has  not  yet  been  discovered  on  any  monu- 
ment or  papyrus-roll.  (Horap.,  p.  194.) 


RAYS    OF    THE   STARS.  129 

with  a  needle  in  a  card,  and  I  have  myself  frequently  ob- 
served both  Canopus  and  Sirius  in  this  manner.  The  same 
thing  occurs  in  telescopic  vision  through  powerful  instru- 
ments, when  the  stars  appear  either  as  intensely  luminous 
points,  or  as  exceedingly  small  disks.  Although  the  fainter 
scintillation  of  the  fixed  stars  in  the  tropics  conveys  a  cer- 
tain impression  of  repose,  a  total  absence  of  stellar  radiation 
would,  in  my  opinion,  impart  a  desolate  aspect  to  the  firma- 
ment, as  seen  by  the  naked  eye.  Illusion  of  the  senses,  op- 
tical illusion,  and  indistinct  vision,  probably  tend  to  augment 
the  splendor  of  the  luminous  canopy  of  heaven.  Arago  long 
since  proposed  the  question  why  fixed  stars  of  the  first  mag- 
nitude, notwithstanding  their  great  intensity  of  light,  can 
not  be  seen  when  rising  above  the- horizon  in  the  same  man- 
ner as  under  similar  circumstances  we  see  the  outer  margin 
of  the  moon's  disk.* 

Even  the  most  perfect  optical  instruments,  and  those  hav- 
ing the  highest  magnifying  powers,  give  to  the  fixed  stars 
spurious  disks  (diametres  factices)  ;  "  the  greater  aperture," 
according  to  Sir  John  Herschel,  "  even  with  the  same  mag- 
nifying power,  giving  the  smaller  disk."t  Occultations  of 
the  stars  by  the  moon's  disk  show  that  the  period  occupied 
in  the  immersion  and  emersion  is  so  transient  that  it  can  not 
be  estimated  at  a  fraction  of  a  second  of  time.  The  frequent 
occurrence  of  the  so-called  adhesion  of  the  immersed  star  to 
the  moon's  disk  is  a  phenomenon  depending  on  inflection  of 
light  in  no  way  connected  with  the  question  of  the  spurious 
diameter  of  the  star.  We  have  already  seen  that  Sir  Will- 
iam Herschel,  with  a  magnifying  power  of  6500,  found  the 
diameter  of  Vega  0"'36.  The  image  of  Arcturus  was  so  di- 
minished in  a  dense  mist  that  the  disk  was  below  0"'2.  It 
is  worthy  of  notice  that,  in  consequence  of  the  illusion  occa- 
sioned by  stellar  radiation,  Kepler  and  Tycho,  before  the  in- 
vention of  the  telescope,  respectively  ascribed  to  Sirius|  a 
diameter  of  4'  and  of  2'  20". 


of  the  Pacific,  that  the  age  of  the  moonTmight  be  determinecl  before 
first  quarter  by  looking  at  it  through  a  piece  of  silk  and  counting  the 
multiplied  images.  Here  we  have  a  phenomenon  of  diffraction  ob- 
served through  fiue  slits. 

t  Outlines,  $  816.  Arago  has  caused  the  spurious  diameter  of  Alde- 
baran  to  increase  from  4"  to  15"  in  the  instrument  by  diminishing  the 
object-glass. 

t  Delambre,  Hist,  de  I'Astr.  Moderne,  torn,  i.,  p.  193 ;  Arago, 
mre,  1842,  p.  366. 

F2 


130  COSMOS. 

The  alternating  light  and  dark  rings  which  surround  the 
email  spurious  disks  of  the  stars  when  magnified  two  or 
three  hundred  times,  and  which  appear  iridescent  when  seen 
through  diaphragms  of  different  form,  are  likewise  the  result 
of  interference  and  diffraction,  as  we  learn  from  the  observ- 
ations of  Arago  and  Airy.  The  smallest  objects  which  can 
be  distinctly  seen  in  the  telescope  as  luminous  points,  may 
be  employed  as  a  test  of  the  perfection  in  construction  and 
illuminating  power  of  optical  instruments,  whether  refractors 
or  reflectors.  Among  these  we  may  reckon  multiple  stars, 
such  as  e  Lyrse,  and  the  fifth  and  sixth  star  discovered  by 
Struve  in  1826,  and  by  Sir  John  Herschel  in  1832,  in  the 
trapezium  of  the  great  nebula  of  Orion,*  forming  the  quad- 
ruple star  6  of  that  constellation. 

A  difference  of  color  in  the  proper  light  of  the  fixed  stars, 
as  well  as  in  the  reflected  light  of  the  planets,  was  recog- 
nized at  a  very  early  period  ;  but  our  knowledge  of  this  re- 
markable phenomenon  has  been  greatly  extended  by  the  aid 
of  telescopic  vision,  more  especially  since  attention  has  been 
so  especially  directed  to  the  double  stars.  We  do  not  here 
allude  to  the  change  of  color  which,  as  already  observed,  ac- 
companies scintillation  even  in  the  whitest  stars,  and  still 
less  to  the  transient  and  generally  red  color  exhibited  by 
stellar  light  near  the  horizon  (a  phenomenon  owing  to  the 
character  of  the  atmospheric  medium  through  which  we  see 
it),  but  to  the  white  or  colored  stellar  light  radiated  from 
each  cosmic  al  body,  in  consequence  of  its  peculiar  luminous 
process,  and  the  different  constitution  of  its  surface.  The 
Greek  astronomers  were  acquainted  with  red  stars  only, 
while  modern  science  has  discovered,  by  the  aid  of  the  tele- 

*  "  Two  excessively  minute  and  very  close  companions,  to  perceive 
loth  of  which  is  one  of  the  severest  tests  which  can  be  applied  to  a  tel- 
escope." (Outlines,  §  837.  Compare  also  Sir  John  Herschel,  Observ- 
ations at  the  Cape,  p.  29 ;  and  Arago,  in  the  Annuaire  pour  1834,  p. 
302-305.)  Among  the  different  planetary  cosmical  bodies  by  which 
the  illuminating  power  of  a  strongly  magnifying  optical  instrument  may 
be  tested,  we  may  mention  the  first  and  fourth  satellites  of  Uranus,  re- 
discovered by  Lassell  and  Otto  Struve  in  1847,  the  two  innermost  and 
the  seventh  satellite  of  Saturn  (Mimas,  Enceladus,  and  Bond's  Hyperi- 
on), and  Neptune's  satellite  discovered  by  Lassell.  The  power  of  pen- 
etrating into  celestial  space  occasioned  Bacon,  in  an  eloquent  passage 
in  praise  of  Galileo,  to  whom  he  erroneously  ascribes  the  invention  of 
telescopes,  to  compare  these  instruments  to  ships  which  cany  men  upon 
an  unknown  ocean :  "  Ut  propriora  exercere  possiut  cum  ccelestibus 
commercia."  (  Works  of  Francis  Bacon,  1740,  vol.  i.,  Novum  Orga- 
num,  p.  361.) 


COLOR    OF    THE    STABS.  131 

Biope,  in  the  radiant  fields  of  the  starry  heaven,  as  in  the 
blossoms  of  the  phanerogamia,  and  in  the  metallic  oxyds, 
almost  all  the  gradations  of  the  prismatic  spectrum  between 
the  extremes  of  refrangibility  of  the  red  and  the  violet  ray. 
Ptolemy  enumerates  in  his  catalogue  of  the  fixed  stars  six 
(vnoictppoi)  fiery  red  stars,  viz.  :*  Arcturus,  Aldebaran,  Pol- 
lux, Antares,  a  Orionis  (in  the  right  shoulder),  and  Sirius. 
Cleomedes  even  compares  Antares  in  Scorpio  with  the  fiery 
red  Mars,f  which  is  called  both  Trvppdf  and  nvpoeidfj^. 

Of  the  six  above-named  stars,  five  still  retain  a  red  or  red- 
dish light.  Pollux  is  still  indicated  as  a  reddish,  but  Castor 
as  a  greenish  star.J  Sirius  therefore  affords  the  only  ex- 
ample of  an  historically  proved  change  of  color,  for  it  has  at 
present  a  perfectly  white  light.  A  great  physical  revolu- 
tion§  must  therefore  have  occurred  at  the  surface  or  in  the 
photosphere  of  this  fixed  star  (or  remote  sun,  as  Aristarchus 

*  The  expression  vnonififtof,  which  Ptolemy  employs  indiscriminate- 
ly to  designate  the  six  stars  named  in  his  catalogue,  implies  a  slightly- 
marked  transition  from  fiery  yellow  to  fiery  red;  it  therefore  refers, 
strictly  speaking,  to  a.  fiery  reddish  color.  He  seems  to  attach  the  gen- 
eral predicate  £av66f, fiery  yellow,  to  all  the  other  fixed  stars.  (Almag., 
viii.,  3d  ed.,  Halma,  torn,  ii.,  p.  94.)  ~K.if>f>6(  is,  according  to  Galen 
(Meth.  Med.,  12),  a  pale  fiery  red  inclining  to  yellow.  Gellius  com- 
pares the  word  with  melinus,  which,  according  to  Servius,  has  the  same 
meaning  as  "  gilvus"  and  "  fulvus."  As  Sirius  is  said  by  Seneca  (Nat. 
Quasi.,  i.,  1)  to  be  redder  than  Mars,  and  belongs  to  the  stars  called  in 
the  Almagest  vnoKifipoi,  there  can  be  no  doubt  that  the  word  implies 
the  predominance,  or,  at  all  events,  a  certain  proportion  of  red  rays. 
The  assertion  that  the  affix  7roi*c/^of ,  which  Aratus,  v.  327,  attaches  to 
Sirius,  has  been  translated  by  Cicero  as  "  rutilus,"  is  erroneous.  Cicero 
says,  indeed,  v.  348: 

"  Namque  pedes  subter  rutilo  cum  lumine  claret, 
Fervidus  ille  Canis  stellarum  luce  refulgena  ;" 

but  "  rutilo  cum  lumine"  is  not  a  translation  of  iroiK&of,  but  the  mere 
addition  of  a  free  translation.  (From  letters  addressed  to  me  by  Pro- 
fessor Franz.)  "  If,"  as  Arago  observes  (Annuaire,  1842,  p.  351),  "  the 
Roman  orator,  in  using  the  term  rutilus,  purposely  departs  from  the 
strict  rendering  of  the  Greek  of  Aratus,  we  must  suppose  that  he  rec- 
ognized the  reddish  character  of  the  light  of  Sirius." 

t  Cleom.,  Cycl.  Theor.,  i.,  ii.,  p.  59. 

t  Madler,  Aslr.,  1849,  s.  391. 

$  Sir  John  Herschel,  in  the  Edinb.  Review,  vol.  87,  1848,  p.  189,  and 
in  Schum.,  A$tr.  Nachr.,  1839,  No.  372:  "  It  seems  much  more  likely 
that  in  Sirius  a  red  color  should  be  the  effect  of  a  medium  interfered, 
than  that  in  the  short  space  of  2000  years  so  vast  a  body  should  have 
actually  undergone  such  a  material  change  in  its  physical  constitution. 
It  may  be  supposed  owing  to  the  existence  of  some  sort  of  cosmical 
cloudiness,  subject  to  internal  movements,  depending  on  causes  of  which 
we  are  ignorant."  (Compare  Arago,  in  the  Annuaire  pour  1842.  p.  350- 
353.) 


132  COSMOS. 

of  Samos  called  the  fixed  ttars)  before  the  process  could  have 
been  disturbed  by  means  of  which  the  less  refrangible  red 
rays  had  obtained  the  preponderance,  through  the  abstraction 
or  absorption  of  other  complementary  rays,  either  in  the  pho- 
tosphere of  the  star  itself,  or  in  the  moving  cosmical  clouds 
by  which  it  is  surrounded.  It  is  to  be  wished  that  the  epoch 
of  the  disappearance  of  the  red  color  of  Sirius  had  been  re- 
corded by  a  definite  reference  to  the  time,  as  this  subject  has 
excited  a  vivid  interest  in  the  minds  of  astronomers  since 
the  great  advance  made  in  modern  optics.  At  the  time  of 
Tycho  Brahe  the  light  of  Sirius  was  undoubtedly  already 
white,  for  when  the  new  star  which  appeared  in  Cassiopeia 
in  1572,  was  observed  in  the  month  of  March,  1573,  to 
change  from  its  previous  dazzling  white  color  to  a  reddish 
hue,  and  again  became  white  in  January,  1574,  the  red  ap- 
pearance of  the  star  was  compared  to  the  color  of  Mars  and 
Aldebaran,  but  not  to  that  of  Sirius.  M.  Sedillot,  or  other 
philologists  conversant  with  Arabic  and  Persian  astronomy, 
may  perhaps  some  day  succeed  in  discovering  evidence  of 
the  earlier  color  of  Sirius,  in  the  periods  intervening  from 
El-Batani  (Albategnius)  and  El-Fergani  (Alfraganus)  to  Ab- 
durrahman Sufi  and  Ebn-Junis  (that  is,  from  880  to  1007), 
and  from  Ebn-Junis  to  Nassir-Eddin  and  Ulugh  Beg  (from 
1007  to  1437). 

El-Fergani  (properly  Mohammed  Ebn-Kethir  El-Fergani), 
who  conducted  astronomical  observations  in  the  middle  of 
the  tenth  century  at  Rakka  (Aracte)  on  the  Euphrates,  in- 
dicates as  red  stars  (stellcn  ruffce,  of  the  old  Latin  translation 
of  1590)  Aldebaran,  and,  singularly  enough,*  Capella,  which 
is  now  yellow,  and  has  scarcely  a  tinge  of  red,  but  he  does 
not  mention  Sirius.  If  at  this  period  Sirius  had  been  no 
longer  red,  it  would  certainly  be  a  striking  fact  that  El-Fer 

*  In  Muhamedis  Alfragani  Chronologica  et  Astronomica  Elementa,  ed. 
Jacobus  Christmannus,  1590,  cap.  22,  p.  97,  we  read,  "  Stella  ruffa  in 
Tauro  Aldebaran ;  Stella  ruffa  in  Geminit  quse  appellatur  Hajok,  hoc 
est  Capra."  Alhajoc,  Aijuk  are,  however,  the  ordinary  names  for  Ca- 
pella Aurigae,  in  the  Arabic  and  Latin  Almagest.  Argelander  justly  ob- 
serves, in  reference  to  this  subject,  that  Ptolemy,  in  the  astrological 
work  (Tcrpu&CAof  cvvTagif),  the  genuine  character  of  which  is  testi- 
fied by  the  style  as  well  as  by  ancient  evidence,  has  associated  planets 
with  stars  according  to  similarity  of  color,  and  has  thus  connected  Mar 
tis  stella,  Quce  urit  slcut  congruit  igneo  ipsius  colori,  with  Auriga?  stella 
or  Capella.  (Compare  Ptol.,  Quadripart.  Construct.,  libri  iv.,  Basil, 
1551,  p.  383.)  Riccioli  (Almageslum  Novum,  ed.  1650,  torn,  i.,  pars  i. 
lib.  6,  cap.  2,  p.  394)  also  reckons  Capella,  together  with  Antares,  Aide 
baran,  and  Arcturus,  among  red  stars. 


SIRIUS.  133 

gani,  who  invariably  follows  Ptolemy,  should  not  here  indi- 
cate the  change  of  color  in  so  celebrated  a  star.  Negative 
proofs  are,  however,  not  often  conclusive,  and,  indeed,  El- 
Fergani  makes  no  reference  in  the  same  passage  to  the  color 
of  Betelgeux  (a  Orionis),  which  is  now  red,  as  it  was  in  the 
age  of  Ptolemy. 

It  has  long  been  acknowledged  that,  of  all  the  brightest 
luminous  fixed  stars  of  heaven,  Sirius  takes  the  first  and  most 
important  place,  no  less  in  a  chronological  point  of  view  than 
through  its  historical  association  with  the  earliest  development 
of  human  civilization  in  the  valley  of  the  Nile.  The  era  of 
Sothis  —  the  heliacal  rising  of  Sothis  (Sirius)  —  on  which  Biot 
has  written  an  admirable  treatise,  indicates,  according  to  the 
most  recent  investigations  of  Lepsius,*  the  complete  arrange- 
ments of  the  Egyptian  calendar  into  those  ancient  epochs,  in- 
cluding nearly  3300  years  before  our  era,  "  when  not  only  the 
summer  solstice,  and,  consequently,  the  beginning  of  the  rise 
of  the  Nile,  but  also  the  heliacal  rising  of  Sothis,  fell  on  the 
day  of  the  first  water-month  (or  the  first  Pachon)."  I  will 
collect  in  a  note  the  most  recent,  and  hitherto  unpublished, 
etymological  researches  on  Sothis  or  Sirius  from  the  Coptic, 
Zend,  Sanscrit,  and  Greek,  which  may,  perhaps,  be  accept- 
able to  those  who,  from  love  for  the  history  of  astronomy,  seek 
in  languages  and  their  affinities  monuments  of  the  earlier 
conditions  of  knowledge.  t 


10-195,  3.  e  compete  arrangement  o  te  gyptan  caen 
referred  to  the  earlier  part  of  the  year  3285  before  our  era,  i.  e., 
a  century  and  a  half  after  the  building  of  the  great  pyramid  of  Ch 
Chufu,  and  940  years  before  the  period  generally  assigned  to  the  D 


See  Chronologie  der^Egypter,  by  Richard  Lepsius,  bd.  i.,  1849,  s. 
190-195,  213.     The  complete  arrangement  of  the  Egyptian  calendar  is 

i.  e.,  about 
f  Cheops- 
the  Deluge. 

(Compare  Cosmos,  vol.  ii.,  p.  114,  115,  note.)  In  the  calculations  based 
on  the  circumstance  of  Colonel  Vyse  having  found  that  the  inclination 
of  the  narrow  subterranean  passage  leading  into  the  interior  of  the  pyr- 
amid very  nearly  corresponded  to  the  angle  26°  15',  which  in  the  time 
of  Cheops  (Chufu)  was  attained  by  the  star  a  Draconis,  which  indicated 
the  pole,  at  its  inferior  culmination  at  Gizeh,  the  date  of  the  building  of 
the  pyramid  is  not  assumed  at  3430  B.C.,  as  given  in  Cosmos  according  to 
Letronne,  but  at  3970  B.C.  (Outlines  of  Astr.,  §  319.)  This  diflerence 
of  540  years  tends  to  strengthen  the  assumption  that  a  Drac.  was  re- 
garded as  the  pole  star,  as  in  3970  it  was  still  at  a  distance  of  3°  44'  from 
the  pole. 

t  I  have  extracted  the  following  observations  from  letters  addressed 
to  me  by  Professor  Lepsius  (February,  1850).  "The  Egyptian  name 
of  Sirius  is  Sothis,  designated  as  a  female  star  ;  hence  q  Hudif  is  identi- 
fied in  Greek  with  the  goddess  Sole  (more  frequently  Sit  in  hieroglyph- 
ics), and  in  the  temple  of  the  great  Ramses  at  Thebes  with  Isis-Sothis 
(Lepsius,  Ckron.  der  ^gypter,bd.  i.,  s.  119,  136).  The  signification  of 
the  root  is  found  in  Coptic,  and  is  allied  with  a  numerous  family  of  words, 


134         .  COSMOS. 

Besides  Sirius,  Vega,  Deneb,  Regulus,  and  Spica  are  at  the 
present  time  decidedly  white ;  and  among  the  small  double 

the  members  of  which,  although  they  apparently  differ  very  widely  from 
each  other,  admit  of  being  arranged  somewhat  in  the  following  order. 
By  the  three-fold  transference  of  the  verbal  signification,  we  obtain  from 
the  original  meaning,  to  throw  out — -projicere  (sagittam,  telurn) — first, 
seminare,  to  sow;  next,  eztendere,  to  extend  or  spread  (as  spun  threads); 
and,  lastly,  what  is  hero  most  important,  to  radiate  light  and  to  shine 
(as  stars  and  fire).  From  this  series  of  ideas  we  may  deduce  the  names 
of  the  divinities,  Satis  (the  female  archer);  Sothis,  the  radiating,  and 
Seth,  the  fiery.  We  may  also  hieroglyphically  explain  sit  or  seti,  the 
arrows  as  well  as  the  ray ;  seta,  to  spin ;  setu,  scattered  seeds.  Sothit 
is  especially  the  brightly  radiating,  the  star  regulating  the  seasons  of 
the  year  and  periods  of  time.  The  small  triangle,  always  represented 
yellow,  which  is  a  symbolical  sign  for  Sothis,  is  used  to  designate  the 
radiating  sun  when  arranged  in  numerous  triple  rows  issuing  in  a  down- 
ward direction  from  the  sun's  disk.  Seth  is  the  fiery  scorching  god,  ia 
contradistinction  to  the  warming,  fructifying  water  of  the  Nile,  the  god- 
dess Satis  who  inundates  the  soil.  She  is  also  the  goddess  of  the  cat- 
aracts, because  the  overflowing  of  the  Nile  began  with  the  appearance 
of  Sothis  in  the  heavens  at  the  summer  solstice.  In  Vettius  Valens  the 
star  itself  is  called  2i?0  instead  of  Sothis ;  but  neither  the  name  nor  the 
subject  admits  of  our  identifying  Thoth  with  Seth  or  Sothis,  as  Ideler 
has  done.  (Handbuch  der  Chronologic,  bd.  i.,  8.  126.)"  (Lepsius,  bd. 
i.,  s.  136.) 

I  will  close  these  observations  taken  from  the  early  Egyptian  periods 
with  some  Hellenic,  Zend,  and  Sanscrit  etymologies :  "  Se/p,  the  sun," 
says  Professor  Franz,  "  is  an  old  root,  differing  only  in  pronunciation 
from  tfep,  &£pog,  heat,  summer,  in  which  we  meet  with  the  same  change 
in  the  vowel  sound  as  in  relpof  and  repof  or  repaf.  The  correctness  of 
these  assigned  relations  of  the  radicals  aelp  and  &ep,  depof,  is  proved 
not  only  by  the  employment  of  tfepetTarof  in  Aratus,  v.  149  (Ideler, 
Sternnamen,  s.  241),  but  also  by  the  later  use  of  the  forms  aeipof,  aei- 
piof,  and  asipivof,  hot,  burning,  derived  from  oeip.  It  is  worthy  of  no- 
tice that  oeipd  or  deipiva  Ifiana  is  used  the  same  as  tiepiva  iftdria,  light 
summer  clothing.  The  form  oelpiof  seems*,  however,  to  have  had  a  wider 
application,  for  it  constitutes  the  ordinary  term  appended  to  all  stars  in- 
fluencing the  summer  heat:  hence,  according  to  the  version  of  the  poet 
Archilochus,  the  sun  was  aeipioc  aarrip,  while  Ibycus  calls  the  stars  gen- 
erally adpia,  luminous.  It  can  not  be  doubted  that  it  is  the  sun  to  which 
Archilochus  refers  in  the  words  iroJUoiif  /*£v  avrov  aeipioe  Karavavel  6£i>f 
kXXufiTruv.  According  to  Hesychius  and  Suidas,  Set'ptof  does  indeed 
signify  both  the  sun  and  the  Dog-star;  but  I  fully  coincide  with  M.  Mar- 
tin, the  new  editor  of  Theon  of  Smyrna,  in  believing  that  the  passage 
of  Hesiod  (Opera  et  Dies,  v.  417)  refers  to  the  sun,  as  maintained  by 
Tzetzes  and  Proclus,  and  not  to  the  Dog-star.  From  the  adjective  oei- 
piof,  which  has  established  itself  as  the  '  epilheton  perpetuum'  of  the 
Dog-star,  we  derive  the  verb  aeipidv,  which  may  be  translated  '  to 
sparkle.'  Aratus,  v.  331,  says  of  Sirius,  bt-£a  aeipiuei, '  it  sparkles  strong- 
ly.' When  standing  alone,  the  word  Setpjyv,  the  Siren,  has  a  totally  dif- 
ferent etymology ;  and  your  conjecture,  that  it  has  merely  an  accidental 
similarity  of  sound  with  the  brightly  shining  star  Sirius,  is  perfectly  well 
founded.  The  opinion  of  those  who,  according  to  Theon  Smyrna^us 
(Liber  de  Astronomia,  1850,  p.  202),  derive  'Zeipfjv  from  oeipid&iv  (a 


THE  COLOR  OF  THE  STARS  135 

stars,  Struve  enumerates  about  300  in  which  both  stars  are 
•white.*  Procyon,  Atair,  the  Pole  Star,  and  more  especially 
ft  Ursae  Min.  have  a  more  or  less  decided  yellow  light.  "We 
have  already  enumerated  among  the  larger  red  or  reddish  stars 
Betelgeux,  Arcturus,  Aldebaran,  Antares,  and  Pollux.  Rum 
ker  finds  y  Crucis  of  a  fine  red  color,  and  my  old  friend,  Cap 
tain  Berard,  who  is  an  admirable  observer,  wrote  from  Mada 
gascar  in  1847  that  he  had  for  some  years  seen  a  Crucis  grow 
ing  red.  The  star  77  Argus,  which  has  been  rendered  cele- 
brated by  Sir  John  Herschel's  observations,  and  to  which  1 
shall  soon  refer  more  circumstantially,  is  undergoing  a  change 
in  color  as  well  as  in  intensity  of  light.  In  the  year  1843, 
Mr.  Mackay  noticed  at  Calcutta  that  this  star  was  similar  in 
color  to  Arcturus,  and  was  therefore  reddish  yellow  ;t  but  in 
letters  from  Santiago  de  Chili,  in  Feb.,  1850,  Lieutenant  Gil- 
liss  speaks  of  it  as  being  of  a  darker  color  than  Mars.  Sir 
John  Herschel,  at  the  conclusion  of  his  Observations  at  the 
Cape,  gives  a  list  of  seventy-six  ruby-colored  small  stars,  of 
the  seventh  to  the  ninth  magnitude,  some  of  which  appear 
in  the  telescope  like  drops  of  blood.  The  majority  of  the  vari- 
able stars  are  also  described  as  red  and  reddish,  f  the  excep- 

moreover  unaccredited  form  of  acipiav'),  is  likewise  entirely  erroneous. 
While  the  motion  of  heat  and  light  is  implied  by  the  expression  aeipiof, 
the  radical  of  the  word  Zeipijv  represents  the  flowing  tones  of  this  phe 
nomenon  of  nature.  It  appears  to  me  probable  that  "Zeipriv  is  connect- 
ed with  elpeiv  (Plato,  Cratyl.,  398,  D,  TO  yap  slpetv  hiyeiv  kar'C),  in  which 
the  original  sharp  aspiration  passed  into  a  hissing  sound."  (From  let 
ters  of  Prof.  Franz  to  me,  January,  1850.) 

The  Greek  2e<p,  the  sun,  easily  admits,  according  to  Bopp,  "  of  be- 
ing associated  with  the  Sanscrit  word  star,  which  does  not  indeed  sig- 
nify the  sun  itself,  but  the  heavens  (as  something  shining').  The  ordi- 
nary Sanscrit  denomination  for  the  sun  is  surya,  a  contraction  of  svdrya, 
which  is  not  used.  The  root  svar  signifies  in  general  to  shine.  The 
Zend  designation  for  the  sun  is  hvare,  with  the  h  instead  of  the  s.  The 
Greek  $fp,  $^pof,  and  i?ep//6f  comes  from  the  Sanscrit  word  gharma 
(N7om.  gharmas'),  warmth,  heat." 

The  acute  editor  of  the  Rigveda,  Max  MQller,  observes,  that  "  the 
special  Indian  astronomical  name  of  the  Dog-star,  Lubdkaka,  which  sig- 
nifies a  hunter,  when  considered  in  reference  to  the  neighboring  con- 
stellation Orion,  seems  to  indicate  an  ancient  Arian  community  of  ideas 
regarding  these  groups  of  stars."  He  is,  moreover,  principally  inclined 
"  to  derive  Zetptof  from  the  Veda  word  rira  (whence  the  adjective  sair- 
ya)  and  the  root  tri,  to  go,  to  wander ;  so  that  the  sun  and  the  bright- 
est of  the  stars,  Sirius,  were  originally  called  wandering  stars."  (Com. 
pare  also  Pott,  Etymologische  Forschungen,  1833,  s.  130.) 

*  Stvuve,  Stellarum  compositarum  Mensuree  Micrometricts,  1837,  ]X 
Ixxiv.  et  Ixxxiii. 

t  Sir  John  Herschel,  Observation!  at  (he  Cape,  p.  34. 

t  Madler's  Attronomie,  s.  436. 


136  SOSMOS. 

tions  being  Algol  in  Caput  Medusae,  ft  Lyraj  and  e  Auriga, 
which  have  a  pure  white  light.  Mira  Ceti,  in  which  a  pe- 
riodical change  of  light  was  first  recognized,  has  a  strong  red- 
dish light  ;*  but  the  variability  observed  in  Algol  and  ft  Lyrse 
proves  that  this  red  color  is  not  a  necessary  condition  of  a 
change  of  light,  since  many  red  stars  are  not  variable.  The 
faintest  stars  in  which  colors  can  be  distinguished  belong,  ac- 
cording to  Struve,  to  the  ninth  and  tenth  magnitudes.  Blue 
stars  were  first  mentioned  by  Mariotte,t  1686,  in  his  Traite 
des  Couleurs.  The  light  of  a  Lyrse  is  bluish  ;  and  a  smaller 
stellar  mass  of  3^-  minutes  in  diameter  in  the  southern  hem- 
isphere consists,  according  to  Dunlop,  of  blue  stars  alone. 
Among  the  double  stars  there  are  many  in  which  the  princi- 
pal star  is  white,  and  the  companion  blue ;  and  some  in  which 
both  stars  have  a  blue  lightj  (as  6  Serp.  and  59  Androm.). 
Occasionally,  as  in  the  stellar  swarm  near  «  of  the  Southern 
Cross,  which  was  mistaken  by  Lacaille  for  a  nebulous  spot, 
more  than  a  hundred  variously-colored  red,  green,  blue,  and 
bluish-green  stars  are  so  closely  thronged  together  that  they 
appear  in  a  powerful  telescope  "  like  a  superb  piece  of  fancy 
jewelry.  "§ 

The  ancients  believed  they  could  recognize  a  remarkable 
symmetry  in  the  arrangement  of  certain  stars  of  the  first 
magnitude.  Thus  their  attention  was  especially  directed  to 
the  four  so-called  regal  stars,  which  are  situated  at  oppo- 
site points  of  the  sphere,  Aldebaran  and  Antares,  Regulus 
and  Fomalhaut.  We  find  this  regular  arrangement,  of 
which  I  have  already  elsewhere  treated,  II  specially  referred 
to  in  a  late  Roman  writer,  Julius  Firmicus  Maternus,1T  who 
belonged  to  the  age  of  Constantine.  The  differences  of 
right  ascension  in  these  regal  stars,  stellce  regales,  are  llh. 
57m.  and  12h.  49m.  The  importance  formerly  attached  to 
this  subject  is  probably  owing  to  opinions  transmitted  from 
the  East,  which  gained  a  footing  in  the  Roman  empire  un- 
der the  Caesars,  together  with  a  itrong  national  predilection 
for  astrology.  The  leg,  or  north  star  of  the  Great  Bear  (the 
celebrated  star  of  the  Bull's  leg  in  the  astronomical  repre- 

*  Cosmos,  vol.  ii.,  p.  330.  t  Arago,  Annuaire  pour  1842,  p.  348. 

t  Struve,  Stella  comp.,  p.  Lxxxii. 

$  Sir  John  Herschel,  Observations  at  the  Cape,  p.  17, 102.  ("  Nebula 
and  Clusters,  No.  3435.") 

II  Humboldt,  Vues  des  CordUleres  et  Monument  des  Peuples  Indigenes 
de  VAmerique,  torn,  ii.,  p.  55. 

IT  Julii  Firmici  Maierni  Astron.,  libri  viii.,  Basil,  1551,  lib.  vi.,  cap 
i.,  p.  150. 


SOUTHERN    STARS.  137 

sentations  of  Dendera,  and  in  the  Egyptian  Book  of  the 
Dead),  is  perhaps  the  star  indicated  in  an  obscure  passage  of 
Job  (ch.  ix.,  ver.  9),  in  which  Arcturus,  Orion,  and  the  Plei- 
ades are  contrasted  with  "  the  chambers  of  the  south,"  and 
in  which  the  four  quarters  of  the  heavens  in  like  manner  are 
indicated  by  these  four  groups.* 

"While  a  large  and  splendid  portion  of  the  southern  heav- 
ens beyond  stars  having  53°  S.  Decl.  were  unknown  in  an- 
cient times,  and  even  in  the  earlier  part  of  the  Middle  Ages, 
the  knowledge  of  the  southern  hemisphere  was  gradually 
completed  about  a  century  before  the  invention  and  appli- 
cation of  the  telescope.  At  the  time  of  Ptolemy  there  were 
visible  on  the  horizon  of  Alexandria,  the  Altar,  the  feet  of 
the  Centaur,  the  Southern  Cross,  then  included  in  the  Cen- 
taur, and,  according  to  Pliny,  also  called  Ccesaris  Thronus, 
in  honor  of  Augustus,!  and  Canopus  (Canobus)  in  Argo, 
which  is  called  Ptolemceon  by  the  scholiast  to  Germanicus.J 

*  Lepsius,  Chronol.  der  ^Egypter,  bd.  i.,  s.  143.  In  the  Hebrew 
text  mention  is  made  of  Asch,  the  giant  (Orion?),  the  many  stars  (the 
Pleiades,  Gemut?),  and  "the  Chambers  of  the  South."  The  Septua- 
gint  ^ives :  6  iroiuv  'EAetd<5a  /cat  'Ecmepov  Kal  'ApKrovpov  /cat  ra^eta 
vorov. 

The  early  English  translators,  like  the  Germans  and  Dutch,  under- 
go >d  the  first  group  referred  to  in  the  verse  to  signify  the  stars  in  the 
Great  Bear.  Thus  we  find  in  Coverdale's  version,  "  He  maketh  the 
waynes  of  heaven,  the  Orions,  the  vii.  stars,  and  the  secret  places  of 
the  south."— Adam  Clarke's  Commentary  on  the  Old  Testament.— (TR.) 

t  Ideler,  Sternnamen,  s.  295. 

t  Martianus  Capella  changes  Ptolemceon  into  Ptolemceus;  both  names 
were  devised  by  the  flatterers  at  the  court  of  the  Egyptian  sovereigns. 
Amerigo  Vespucci  thought  he  had  seen  three  Canopi,  one  of  which  was 
quite  dark  (fosco),  Canopus  ingens  et  niger  of  the  Latin  translation ;  most 
probably  one  of  the  black  coal-sacks.  (Humboldt,  Examen  Crit.  de 
la  Geogr.,  torn,  v.,  p.  227,  229.)  In  the  above-named  Elem.  Chronol. 
et  Astron.  by  El-Fergani  (p.  100),  it  is  stated  that  the  Christian  pilgrims 
used  to  call  the  Sohel  of  the  Arabs  (Canopus)  the  star  of  St.  Catharine, 
because  they  had  the  gratification  of  observing  it,  and  admiring  it  as  a 
guiding  star  when  they  journeyed  from  Gaza  to  Mount  Sinai.  In  a  fine 
episode  to  the  Ramayana,  the  oldest  heroic  poem  of  Indian  antiquity, 
the  stars  in  the  vicinity  of  the  South  Pole  are  declared  for  a  singular 
reason  to  have  been  more  recently  created  than  the  northern.  When 
Brahminical  Indians  were  emigrating  from  the  northwest  to  the  coun 
tries  around  the  Ganges,  from  the  30th  degree  of  north  latitude  to  the 
lands  of  the  tropics,  where  they  subjected  the  original  inhabitants  to 
their  dominion,  they  saw  unknown  stars  rising  above  the  horizon  as 
they  advanced  toward  Ceylon.  In  accordance  with  ancient  practice, 
they  combined  these  stars  into  new  constellations.  A  bold  fiction  rep- 
resented the  later-seen  stars  as  having  been  subsequently  created  by 
the  miraculous  power  of  Visvamitra,  who  threatened  "  the  ancient  gods 
that  he  would  overcome  the  northern  hemisphere  with  his  more  richly- 


138  COSMOS. 

In  the  catalogue  of  the  Almagest,  Achernar,  a  star  of  the 
first  magnitude,  the  last  in  Eridanus  (Achir  el-nahr,  in 
Arabic),  is  also  given,  although  it  was  9°  below  the  hori- 
zon. A  report  of  the  existence  of  this  star  must  therefore 
have  reached  Ptolemy  through  the  medium  of  those  who  had 
made  voyages  to  the  southern  parts  of  the  Red  Sea,  or  be- 
tween Ocelis  and  the  Malabar  emporium,  Muziris.*  Though 
improvements  in  the  art  of  navigation  led  Diego  Cam,  to- 
gether with  Martin  Behaim,  along  the  western  coasts  of  Af- 
rica, as  early  as  1484,  and  carried  Bartholomew  Diaz  in 
1487,  and  Gama  in  1497  (on  his  way  to  the  East  Indies), 
far  beyond  the  equator,  into  the  Antarctic  Seas,  as  far  as 
35°  south  lat.,  the  first  special  notice  of  the  large  stars  and 
nebulous  spots,  the  first  description  of  the  "  Magellanic 
clouds"  and  the  "  coal-sacks,"  and  even  the  fame  of  "  the 
wonders  of  the  heavens  not  seen  in  the  Mediterranean,"  be- 
long to  the  epoch  of  Vicente  Yanez  Pinzon,  Amerigo  Ves- 
pucci, and  Andrea  Corsali,  between  1500  and  1515.  The 
distances  of  the  stars  of  the  southern  hemisphere  were  meas- 
ured at  the  close  of  the  sixteenth  and  the  beginning  of  the 
seventeenth  century. t 

Laws  of  relative  density  in  the  distribution  of  the  fixed 
stars  in  the  vault  of  heaven  first  began  to  be  recognized 
when  Sir  William  Herschel,  in  the  year  1785,  conceived 
the  happy  idea  of  counting  the  number  of  stars  which  passed 

starred  southern  hemisphere."  (A.  W.  von  Schlegel,  in  the  Zeilschrift 
fur  die  Kunde  des  Morgcnlandes,  bd.  i.,  B.  240.)  While  this  Indian 
myth  figuratively  depicts  the  astonishment  excited  in  wandering  na- 
'  ,  by  the  aspect  of  i 


tions  by  the  aspect  of  a  new  heaven  (as  the  celebrated  Spanish  poet, 
Garcilaso  de  la  Vega,  says  of  travelers,  "  they  change  at  once  their  coun- 
try and  stars,"  mttdan  de  pays  y  de  estrellas),  we  are  powerfully  re- 
minded of  the  impression  that  must  have  been  excited,  even  in  the 
rudest  nations,  when,  at  a  certain  part  of  the  earth's  surface,  they  ob- 
served large,  hitherto  unseen  stars  appear  in  the  horizon,  as  those  in 
the  feet  of  the  Centaur,  in  the  Southern  Cross,  in  Eridauus  or  in  Argo, 
while  those  with  which  they  had  been  long  familiar  at  home  wholly 
disappeared.  The  fixed  stars  advance  toward  us,  and  again  recede, 
owing  to  the  precession  of  the  equinoxes.  We  have  already  mentioned 
that  the  Southern  Cross  was  7°  above  the  horizon,  in  the  countries 
around  the  Baltic,  2900  years  before  our  era;  at  a  time,  therefore,  when 
the  great  pyramids  had  already  existed  five  hundred  years.  (Compare 
Cosmog,  vol.  i.,  p.  149,  and  vol.  ii.,  p.  282.)  "  Cauopus,  on  the  other 
hand,  can  never  have  been  visible  at  Berlin,  as  its  distance  from  the 
south  pole  of  the  ecliptic  amounts  to  only  14°.  It  would  have  required 
a  distance  of  1°  more  to  bring  it  within  the  limits  of  visibility  for  our 
horizon."  *  Cosmos,  vol.  ii.,  p.  571,  572. 

t  Olbers,  in  Schumacher's  Jahrb.f&r  1840,  s.249,  and  Cosmos,  vol.  i., 
p.  51. 


DISTRIBUTION   OF   STARS.  139 

at  different  heights  and  in  various  directions  over  the  field 
of  view,  of  15'  in  diameter,  of  his  twenty-feet  reflecting  tel- 
escope. Frequent  reference  has  already  been  made  in  the 
present  work  to  his  laborious  process  of  "  gauging  the  heav- 
ens." The  field  of  view  each  time  embraced  only  ^^TV^?tn 
of  the  whole  heavens ;  and  it  would  therefore  require,  ac- 
cording to  Struve,  eighty-three  years  to  gauge  the  whole 
sphere  by  a  similar  process.*  In  investigations  of  the  par- 
tial distribution  of  stars,  we  must  specially  consider  the  class 
of  magnitude  to  which  they  photometrically  belong.  If  we 
limit  our  attention  to  the  bright  stars  of  the  first  three  or 
four  classes  of  magnitudes,  we  shall  find  them  distributed  on 
the  whole  with  tolerable  uniformity, t  although  in  the  south- 
ern hemisphere,  from  £  Orionis  to  a  Crucis,  they  are  locally 
crowded  together  in  a  splendid  zone  in  the  direction  of  a 
great  circle.  The  various  opinions  expressed  by  different 
travelers  on  the  relative  beauty  of  the  northern  and  south- 
ern hemispheres,  frequently,  I  believe,  depends  wholly  on  the 
circumstance  that  some  of  these  observers  have  visited  the 
southern  regions  at  a  period  of  the  year  when  the  finest  por- 
tion of  the  constellations  culminate  in  the  daytime.  It  fol- 
lows, from  the  gaugings  of  the  two  Herschels  in  the  north- 
ern and  southern  hemispheres,  that  the  fixed  stars  from  the 
fifth  and  sixth  to  the  tenth  and  fifteenth  magnitudes  (par- 
ticularly, therefore,  telescopic  stars)  increase  regularly  in 
density  as  we  approach  the  galactic  circle  (6  yaAafmf  KV- 
/cAof)  ;  and  that  there  are  therefore  poles  rich  in  stars,  and 
others  poor  in  stars,  the  latter  being  at  right  angles  to  the 
principal  axis  of  the  Milky  Way.  The  density  of  the  stellar 
light  is  at  its  minimum  at  the  poles  of  the  galactic  circle ; 
and  it  increases  in  all  directions,  at  first  slowly,  and  then  rap- 
idly, in  proportion  to  the  increased  galactic  polar  distance. 
By  an  ingenious  and  careful  consideration  of  the  results 
of  the  gauges  already  made,  Struve  found  that  on  the  average 
there  are  29-4  tunes  (nearly  30  times)  as  many  stars  in  the 
center  of  the  Milky  Way  as  in  regions  surrounding  the  ga- 
lactic poles.  In  northern  galactic  polar  distances  of  0°,  30°, 
60°,  75°,  and  90°,  the  relative  numbers  of  the  stars  in  a  tel- 
escopic field  of  vision  of  15'  diameter  are  4-15,  6-52,  17'68, 
30-30,  and  122-00.  Notwithstanding  the  great  similarity 
in  the  law  of  increase  in  the  abundance  of  the  stars,  we 
again  find  in  the  comparison  of  these  zones  an  absolute  pre- 

*  Etudes  tfAstr.  Stellaire,  note  74,  p.  31. 
t  Outlines  of  Astr.,  §  785 


140  COSMOS. 

ponderance*  on  the  side  of  the  more  beautiful  southern 
heavens. 

When  in  1843  I  requested  Captain  Schwinck  (of  the  En- 
gineers) to  communicate  to  me  the  distribution  according  to 
right  ascension  of  the  12,148  stars  (from  the  first  to  the  sev- 
enth inclusive),  which,  at  Bessel's  suggestion,  he  had  noted 
in  his  Mappa  Caslestis,  he  found  in  four  groups — 
Right  Ascension,     50°  to  140°       3147  stars. 
140°       230°       2627     " 
230°       320°      3523     " 
320°         50°      2851     " 

These  groups  correspond  with  the  more  exact  results  of  the 
Etudes  Stellaires,  according  to  which  the  maxima  of  stars 
of  the  first  to  the  ninth  magnitude  occur  in  the  right  ascen- 
sion 6h.  40m.  and.  I8h.  40m.,  and  the  minima  in  the  right 
ascension  of  Ih.  30m.  and  13h.  30m. t 

It  is  essential  that,  in  reference  to  the  conjectural  struc- 
ture of  the  universe  and  to  the  position  or  depth  of  these 
strata  of  conglomerate  matter,  we  should  distinguish  among 
the  countless  number  of  stars  with  which  the  heavens  are 
studded,  those  which  are  scattered  sporadically,  and  those 
which  occur  in  separate,  independent,  and  crowded  groups. 
The  latter  are  the  so-called  stellar  dusters  or  swarms,  which 
frequently  contain  thousands  of  telescopic  stars  in  recogniza- 
ble relations  to  each  other,  and  which  appear  to  the  unaided 
eye  as  round  nebulae,  shining  like  comets.  These  are,  the 
nebulous  stars  of  EratosthenesJ  and  Ptolemy,  the  nebulosce 
of  the  Alphonsine  Tables  in  1483,  and  the  same  of  which 
Galileo  said  in  the  Nuncius  Sidereus,  "  Sicut  areolee  spar- 
sim  per  sethera  subfulgent." 

These  clusters  of  stars  are  either  scattered  separately 
throughout  the  heavens,  or  closely  and  irregularly  crowded 
together,  in  strata,  as  it  were,  in  the  Milky  Way,  and  in  the 
Magellanic  clouds.  The  greatest  accumulation  of  globular 
clusters,  and  the  most  important  in  reference  to  the  config- 
uration of  the  galactic  circle,  occurs  in  a  region  of  the  south- 
ern heavens^  between  Corona  Australis,  Sagittarius,  the 

*  Op.  cit.,  §  795,  796 ;  Struve,  Eludes  cTAstr.  Stell.,  p.  66,  73  (and 
note  75). 

t  Struve,  p.  59.  Schwinck  finds  in  his  maps,  R.  A.  0°-90°,  2858 
stars;  R.  A.  9QO-1800,  3011  stars;  R.  A.  180°-270°,  2688  stars;  R.  A 
270°-360°,  3591  stars ;  sura  total,  12,148  stars  to  the  seventh  magnitude 

t  On  the  nebula  in  the  right  hand  of  Perseus  (near  the  hilt  of  his 
sword),  see  Eratosth.,  Catant.,  c.  22,  p.  51,  Schaubach. 

$  John  Herschel's  Observations  at  the  Cape,  $  105,  p.  136. 


CLUSTERS    OF    STARS.  141 

tail  of  Scorpio,  and  the  Altar  (R.  A.  16h.  45m.-l9h.).  All 
clusters  in  and  near  the  Milky  Way  are  not,  however,  round 
and  globular ;  there  are  many  of  irregular  outline,  with  but 
few  stars  and  not  a  very  dense  center.  In  many  globular 
clusters  the  stars  are  uniform  in  magnitude,  in  others  they 
vary.  In  some  few  cases  they  exhibit  a  fine  reddish  cen- 
tral star*  (R.  A.  2h.  10m. ;  N  Decl.  56°  21').  It  is  a  dif- 
ficult problem  in  dynamics  to  understand  how  such  island- 
worlds,  with  their  multitude  of  suns,  can  rotate  free  and  un 
disturbed.  Nebulous  spots  and  clusters  of  stars  appear  sub- 
ject to  different  laws  in  their  local  distribution,  although  the 
former  are  now  very  generally  assumed  to  consist  of  very 
small  and  still  more  remote  stars.  The  recognition  of  these 
laws  must  specially  modify  the  conjectures  entertained  of 
what  has  been  boldly  termed  the  "  structure  of  the  heav- 
ens." It  is,  moreover,  worthy  of  notice,  that,  with  an  in- 
strument of  equal  aperture  and  magnifying  power,  round 
nebulous  spots  are  more  easily  resolved  into  clusters  of  stars 
than  oval  ones.f 

I  will  content  myself  with  naming  the  following  among 
the  isolated  systems  of  clusters  and  swarms  of  stars. 

The  Pleiades  :  doubtless  known  to  the  rudest  nations  from 
the  earliest  times  ;  the  mariner's  stars — Pleias,  and  rov 
rrAetv  (from  TrAetv,  to  sail),  according  to  the  etymology  of 
the  old  scholiast  of  Aratus,  who  is  probably  more  correct  than 
those  modern  writers  who  would  derive  the  name  from  rrAeof, 
plenty.  The  navigation  of  the  Mediterranean  lasted  from 
May  to  the  beginning  of  November,  from  the  early  rising  to 
the  early  setting  of  the  Pbiades. 

Prsesepe  in  Cancer  :  according  to  Pliny,  nubecula  quam 
Prczsepia  vacant  inter  Asellos,  a  ve</>eA*ov  of  the  Pseudo^ 
Eratosthenes. 

The  cluster  of  stars  on  the  sword-hilt  of  Perseus,  frequent- 
ly mentioned  by  Greek  astronomers. 

Coma  Berenices,  like  the  three  former,  visible  to  the  naked 
eye. 

A  cluster  of  stars  near  Arcturus  (No.  1663),  telescopic  : 
R.  A.  I3h.  34m.  12s.,  N.  Decl.  29°  14' ;  more  than  a  thousand 
stars  from  the  tenth  to  the  twelfth  magnitude. 

Cluster  of  stars  between  77  and  £  Herculis,  visible  to  the 
naked  eye  in  clear  nights.  A  magnificent  object  in  the  tel- 
escope (No.  1968),  with  a  singular  radiating  margin  ;  R.  A. 

»  Outlines,  $  864-869,  p.  591-596;  Madler's  Astr.,  s.  764. 
t  Observation  at  the  Cape,  $  29,  p.  19. 


142  COSMOS. 

16h.  35m.  37s.,  N.  Dccl.  36°  47' ;  first  described  by  Halley 
in  1714. 

A  cluster  of  stars  near  w  Centauri ;  described  by  Halley  as 
early  as  1677  ;  appearing  to  the  naked  eye  as  a  round  cometic 
object,  almost  as  bright  as  a  star  of  the  fourth  or  fifth  magni- 
tude ;  in  powerful  instruments  it  appears  composed  of  count- 
less stars  of  the  thirteenth  to  the  fifteenth  magnitude,  crowd- 
ed together  and  most  dense  toward  the  center;  R.  A.  13h. 
16m.  38s.,  S.  Decl.  46°  35' ;  No.  3504  in  Sir  John  Herschel's 
catalogue  of  the  clusters  of  the  southern  hemisphere,  15'  in 
diameter.  (Observations  at  the  Cape,  p.  21, 105 ;  Outlines 
ofAstr.,  p.  595.) 

Cluster  of  stars  near  K  of  the  Southern  Cross  (No.  3435), 
composed  of  many-colored  small  stars  from  the  twelfth  to  the 
sixteenth  magnitude,  distributed  over  an  area  of  Jj-th  of  a 
square  degree  ;  a  nebulous  star,  according  to  Lacaille,  but 
so  completely  resolved  by  Sir  John  Herschel  that  no  nebulous 
mass  remained  ;  the  central  star  deep  red.  (Observations 
at  the  Cape,  p.  17,  102,  pi.  i.,  fig.  2.) 

Cluster  of  stars,  47  Toucani,  Bode  ;  No.  2322  of  Sir  John 
Herschel's  catalogue,  one  of  the  most  remarkable  objects  in 
the  southern  heavens.  I  was  myself  deceived  by  it  for  sev- 
eral evenings,  imagining  it  to  be  a  comet,  when,  on  my  ar- 
rival at  Peru,  I  saw  it  in  12°  south  lat.  rise  high  above  the 
horizon.  The  visibility  of  this  cluster  to  the  naked  eye  is  in- 
creased by  the  circumstance  that,  although  in  the  vicinity 
of  the  lesser  Magellanic  cloud,  it  is  situated  in  a  part  of  the 
heavens  containing  no  stars,  and  is  from  15'  to  20'  in  diam- 
eter. It  is  of  a  pale  rose  color  in  the  interior,  concentrically 
inclosed  by  a  white  margin  composed  of  small  stars  (four- 
teenth to  sixteenth  magnitude)  of  about  the  same  magnitude, 
and  presenting  all  the  characteristics  of  the  globular  form.* 

A  cluster  of  stars  in  Andromeda's  girdle,  near  v  of  this  con- 
stellation. The  resolution  of  this  celebrated  nebula  into  small 
stars,  upward  of  1500  of  which  have  been  vecognized,  apper- 
tains to  the  most  remarkable  discoveries  in  the  observing  as- 
tronomy of  the  present  day.  The  merit  of  this  discovery  is  due 
to  Mr.  George  Bond,  assistant  astronomerf  at  the  Observatory 

*  "  A  stupendous  object — a  most  magnificent  glolular  cluster,"  says 
Sir  John  Herschel,  "  completely  insulated,  upon  a  ground  of  the  sky  per- 
fectly black  throughout  the  whole  breadth  of  the  sweep." — Observations 
at  the  Cape,  p.  18  and  51,  PI.  iii.,  fig.  1 ;  Outlines,  $  895,  p.  615. 

t  Bond,  in  the  Memoirs  of  the  American  Academy  of  Arts  and  Sciences, 
iiew  series,  vol.  iii.,  p.  75. 


CLUSTERS  9F  STARS.  143 

of  Cambridge,  United  States  (March,  1848),  and  testifies  to 
the  admirable  illuminating  power  of  the  refractor  of  that  Ob- 
servatory, which  has  an  object-glass  fifteen  inches  in  diam- 
eter ;  since  even  a  reflector  with  a  speculum  of  eighteen  inch 
es  in  diameter  did  not  reveal  "  a  trace  of  the  presence  of  a 
star."*  Although  it  is  probable  that  the  cluster  in  Adrom- 
eda  was,  at  the  close  of  the  tenth  century,  already  recorded 
as  a  nebula  of  oval  form,  it  is  more  certain  that  Simon  Ma- 
rius  (Mayer  of  Guntzenhausen),  the  same  who  first  observed 
the  change  of  color  in  scintillation,!  perceived  it  on  the  1 5th 
of  December,  1612  ;  and  that  he  was  the  first  who  described 
it  circumstantially  as  a  new  starless  and  wonderful  cosmical 
body  unknown  to  Tycho  Brahe.  Half  a  century  later,  Bouil- 
laud,  the  author  of  Astronomia  Philolaica,  occupied  himself 
with  the  same  subject.  This  cluster  of  stars,  which  is  2^-° 
in  length  and  more  than  1°  in  breath,  is  specially  distinguish- 
ed by  two  remarkable  very  narrow  black  streaks,  parallel  to 
each  other,  and  to  the  longer  axis  of  the  cluster,  which,  ac- 
cording to  Bond's  investigations,  traverse  the  whole  length 
like  fissures.  This  configuration  vividly  reminds  us  of  the 
singular  longitudinal  fissure  in  an  unresolved  nebula  of  the 
southern  hemisphere,  No.  3501,  which  has  been  described 
and  figured  by  Sir  John  Herschel.  (Observations  at  the 
Cape,  p.  20,  105,  pi.  iv.,  fig.  2.) 

Notwithstanding  the  important  discoveries  for  which  we 
are  indebted  to  Lord  Rosse  and  his  colossal  telescope,  I  have 
not  included  the  great  nebula  in  Orion's  belt  in  this  selection 
of  remarkable  clusters  of  stars,  as  it  appeared  to  me  more  ap- 
propriate to  consider  those  portions  of  it  which  have  been  re- 
solved in  the  section  on  Nebulae. 

The  greatest  accumulation  of  clusters  of  stars,  although 
by  no  means  of  nebulas,  occurs  in  the  Milky  WayJ  (Galaxias, 

*  Outlines,  $  874,  p.  601. 

t  Delambre,  Hist,  de  VAstr.  Moderne,  t.  i.,  p.  697. 

t  We  are  indebted  for  the  first  and  only  complete  description  of  the 
Milky  Way,  in  both  hemispheres,  to  Sir  John  Herschel,  in  his  Results 
of  Astronomical  Observations,  made  during  the  Years  1834-1838,  at  the 
Cape  of  Good  Hope,  §  316-335,  and  still  more  recently  in  the  Outlines 
of  Astronomy,  §  787-799.  Throughout  the  whole  of  that  section  of  the 
Cosmos  which  treats  of  the  directions,  ramifications,  and  various  con- 
tents of  the  Milky  Way,  I  have  exclusively  followed  the  above-named 
astronomer  and  physicist.  (Compare  also  Struve,  Etudes  d'Astr.  Stel- 
laire,  p.  35-79 ;  Madler,  Ast.,  1849,  §  213 ;  Cosmos,  vol.  i.,  p.  103,  150.) 
I  need  scarcely  here  remark  that  in  my  description  of  the  Milky  Way, 
in  order  not  to  confuse  certainties  with  uncertainties,  I  have  not  refer- 
red to  what  I  had  myself  observed  with  instruments  of  a  very  inferior 


144  COSMOS. 

the  celestial  river  of  the  Arabs*),  which  forms  almost  a  great 
circle  of  the  sphere,  and  is  inclined  to  the  equator  at  an  an- 
gle of  63°.  The  poles  of  the  Milky  Way  are  situated  in  Right 
Ascension  12h.  47m.,  N.  Decl.  27°  ;  and  R.  A.  Oh.  47m.,  S. 
Decl.  27°  ;  the  south  galactic  pole  therefore  lies  near  Coma 
Berenices,  and  the  northern  between  Phoenix  and  Cetus. 
While  all  planetary  local  relations  are  referred  to  the  eclip- 
tic— the  great  circle  in  which  the  plane  of  the  sun's  path  in- 
tersects the  sphere — we  may  as  conveniently  refer  many  of 
the  local  relations  of  the  fixed  stars,  as,  for  instance,  that  of 
their  accumulation  or  grouping,  to  the  nearly  complete  circle 
of  the  Milky  Way.  Considered  in  this  light,  the  latter  is  to 
the  sidereal  world  what  the  ecliptic  is  to  the  planetary  world 
of  our  solar  system.  The  Milky  Way  cuts  the  equator  in 
Monoceros,  between  Procyon  and  Sinus,  R.  A.  Gh.  54m.  (for 
1800),  and  in  the  left  hand  of  Antinous,  R.  A.  19h.  15m. 
The  Milky  Way,  therefore,  divides  the  celestial  sphere  into 
two  somewhat  unequal  halves,  whose  areas  are  nearly  as  8 
to  9.  In  the  smaller  portion  lies  the  vernal  solstice.  The 
Milky  Way  varies  considerably  in  breadth  in  different  parts 
of  its  course.f  At  its  narrowest,  and,  at  the  same  time,  most 
brilliant  portion,  between  the  prow  of  Argo  and  the  Cross, 
and  nearest  to  the  Antarctic  pole,  its  width  is  scarcely  3°  or 
4°  ;  at  other  parts  it  is  16°,  and  in  its  divided  portion,  be- 
tween Ophiuchus  and  Antinous,  as  much  as  22°.$  William 
Herschel  has  observed  that,  judging  from  his  star-gaugings, 
the  Milky  Way  would  appear  in  many  regions  to  have  6°  or 
7°  greater  width  than  we  should  be  disposed  to  ascribe  to 
it  from  the  extent  of  stellar  brightness  visible  to  the  naked 
eye."§ 

Huygens,  who  examined  the  Milky  Way  with  his  twenty- 
three  feet  refractor,  declared,  as  early  as  the  year  1656,  that 
the  milky  whiteness  of  the  whole  Galactic  zone  was  not  to 

illuminating  power,  in  reference  to  the  very  great  inequality  of  the 
light  of  the  whole  zone,  during  my  long  residence  iu  the  southern  hem- 
isphere, and  which  I  have  recorded  in  my  journals. 

*  The  comparison  of  the  ramified  Milky  Way  with  a  celestial  river 
led  the  Arabs  to  designate  parts  of  the  constellation  of  Sagittarius,  whose 
bow  falls  in  a  region  rich  in  stars,  as  the  cattle  going  to  drink,  and  to 
associate  with  them  the  ostrich,  which  has  so  little  need  of  water.  (Ide- 
ler,  Untersuchungen  uber  den  Ursprung  und  die  Dedeutung  der  Sternna* 
men,  §  78,  183,  and  187  ;  Niebuhr,  Beschreibung  von  Arabien,  e.  112.) 

t  Outlines,  p.  529;  Schubert,  Ast.,  th.  iii.,  s.  71. 

t  Struve,  Etudes  d'Astr.  Stellaire,  p.  41. 

$  Cosmos,  vol.  L,  p.  150. 


MILKY    WAY.  145 

be  ascribed  to  irresolvable  nebulosity.  A  more  careful  ap- 
plication of  reflecting  telescopes  of  great  dimensions  and  pow- 
er of  light  has  since  proved,  with  more  certainty,  the  cor 
rectness  of  the  conjectures  advanced  by  Democritus  and  Ma- 
nilius,  in  reference  to  the  ancient  path  of  Phaeton,  that  this 
milky  glimmering  light  was  solely  owing  to  the  accumu 
lated  strata  of  small  stars,  and  not  to  the  scantily  inter 
spersed  nebulae.  This  effusion  of  light  is  the  same  at  points 
where  the  whole  can  be  perfectly  resolved  into  stars,  and 
even  in  stars  which  are  projected  on  a  black  ground,  wholly 
free  from  nebulous  vapor.*  It  is  a  remarkable  feature  of 
the  Milky  "Way  that  it  should  so  rarely  exhibit  any  globular 
clusters  and  nebulous  spots  of  a  regular  or  oval  form  ;t  while 
both  are  met  with  in  great  numbers  at  a  remote  distance 
from  it ;  as,  for  instance,  in  the  Magellanic  clouds,  where 
isolated  stars,  globular  clusters  in  all  conditions  of  condensa- 
tion, and  nebulous  spots  of  a  definite  oval  or  a  wholly  irreg- 
ular form,  are  intermingled.  A  remarkable  exception  to 
the  rarity  of  globular  clusters  in  the  Milky  Way  occurs  in  a 
region  between  R.  A.  16h.  45m.  and  18h.  44m.,  between  the 
Altar,  the  Southern  Crown,  the  head  and  body  of  Sagitta- 
rius, and  the  tail  of  the  Scorpion.^  We  even  find  between 
£  and  6  of  the  latter  one  of  those  annular  nebulae,  which  are 
of  such  extremely  rare  occurrence  in  the  southern  hemi- 
sphere. 

In  the  field  of  view  of  powerful  telescopes  (and  we  must 
remember  that,  according  to  the  calculations  of  Sir  William 

*  "Stars  standing  on  a  clear  black  ground."  (Observations  at  the 
Cape,  p.  391.)  "  This  remarkable  belt  (the  Milky  Way,  when  exam- 
ined through  powerful  telescopes)  is  found  (wonderful  to  relate !)  to 
consist  entirely  of  stars  scattered  by  millions,  like  glittering  dust  on  the 
)lack  ground  of  the  general  heavens." — Outlines,  p.  182,  537,  and  539. 

t  "  Globular  clusters,  excepting  in  one  region  of  small  extent  (be- 
tween 16h.  45m.  and  19h.  in  R.  A.),  and  pebulce  of  regular  elliptic 
forms,  are  comparatively  rare  in  the  Milky  Way,  and  are  found  con- 
gregated in  the  greatest  abundance  in  a  part  of  the  heavens  the  most 
remote  possible  from  that  circle."  (Outlines,  p.  614.)  Huygens  him- 
self, as  early  as  1656,  had  remarked  the  absence  of  nebulosity  and  of 
all  nebulous  spots  in  the  Milky  Way.  In  the  same  place  where  he 
mentions  th  3  first  discovery  and  delineation  of  the  great  nebulous  spots 
in  the  belt  of  Orion,  by  a  twenty-eight  feet  refractor  (1656),  he  says 
(as  I  have  already  remarked  in  vol.  h.,  p.  330,  and  note),  viam  lacteam 
perspicillis  inspectam  nullas  habere  nebulas,  and  that  the  Milky  Way,  like 
all  that  has  been  regarded  as  nebulous  stars,  is  a  great  cluster  of  stars 
The  passage  is  to  be  found  in  Hugenii  Opera  varia,  1724,  p.  540. 

t  Observations  at  the  Cape,  $  105, 107,  and  328.  On  the  annular  nel> 
ulsB,  No.  3686,  see  p.  114. 

VOL.  Ill—  ? 


146  .     COSMOS. 

Herschel,  a  twenty-feet  instrument  penetrates  900,  and  a 
forty-feet  one  2800  distances  of  Sinus),  the  Milky  Way  ap- 
pears as  diversified  in  its  sidereal  contents  as  it  is  irregular 
and  indefinite  in  its  outlines  and  limits  when  seen  by  the 
unaided  eye.  While  in  some  parts  the  Milky  Way  exhibits, 
throughout  a  large  space,  the  greatest  uniformity  in  the  light 
and  apparent  magnitudes  of  the  stars,  in  others  the  most 
brilliant  patches  of  closely-crowded  luminous  points  are  in- 
terrupted by  granular  or  reticular  darker*  intervals  contain- 
ing but  few  stars  ;  and  in  some  of  these  intervals  in  the  in- 
terior of  the  Galaxy  not  the  smallest  star  (of  the  18m.  or 
20m.)  is  to  be  discovered.  It  almost  seems  as  though,  in 
these  regions,  we  actually  saw  through  the  whole  starry 
stratum  of  the  Milky  Way.  In  gauging  with  a  field  of  view 
of  15'  diameter,  fields  presenting  on  an  average  forty  or  fifty 
stars  are  almost  immediately  succeeded  by  others  exhibiting 
from  400  to  500.  Stars  of  the  higher  magnitudes  often  oc- 
cur in  the  midst  of  the  most  minute  telescopic  stars,  while 
all  the  intermediate  classes  are  absent.  Perhaps  those  stars 
which  we  regard  as  belonging  to  the  lowest  order  of  mag- 
nitudes do  not  always  appear  as  such,  solely  on  account  of 
their  enormous  distance,  but  also  because  they  actually  have 
a  smaller  volume  and  less  considerable  development  of  light. 
In  order  rightly  to  comprehend  the  contrast  presented  by 
the  greater  brilliancy,  abundance,  or  paucity  of  stars,  it  will 
be  necessary  to  compare  regions  most  widely  separated  from 
each  other.  The  maximum  of  the  accumulation  and  the 
greatest  luster  of  stars  are  to  be  found  between  the  prow  of 
Argo  and  Sagittarius,  or,  to  speak  more  exactly,  between  the 
Altar,  the  tail  of  the  Scorpion,  the  hand  and  bow  of  Sagit- 
tarius, and  the  right  foot  of  Ophiuchus.  "  No  region  of  the 
heavens  is  fuller  of  objects,  beautiful  and  remarkable  in 
themselves,  and  rendered  still  more  so  by  their  mode  of  as- 
sociation" and  grouping. t  Next  in  brightness  to  this  por- 

*  "  Intervals  absolutely  dark  and  completely  void  of  any  ttar  of  the 
smallest  telescopic  magnitude." — Outlines,  p.  536. 

t  "  No  region  of  the  heavens  is  fuller  of  objects,  beautiful  and  re- 
markable  in  themselves,  and  rendered  still  more  so  by  their  mode  of 
association,  and  by  the  peculiar  features  assumed  by  the  Milky  Way, 
which  are  without  a  parallel  in  any  other  part  of  its  course."— '•Observ- 
ations at  the  Cape,  p.  386.  This  vivid  description  of  Sir  John  Hersche] 
entirely  coincides  with  the  impressions  I  have  myself  experienced. 
Capt.  Jacob,  of  the  Bombay  Engineers,  in  speaking  of  the  intensity  of 
light  in  the  Milky  Way,  in  the  vicinity  of  the  Southern  Cross,  remarks 
with  striking  truth,  "  Such  is  the  general  blaze  of  starlight  near  the 
Cross  from  that  part  of  the  sky,  that  a  person  is  immediately  made 


MILKY    WAY.  147 

tion  of  the  southern  heavens  is  the  pleasing  and  richly-star- 
red region  of  our  northern  hemisphere  in  Aquila  and  Cyg- 
nus,  where  the  Milky  Way  branches  off  in  different  direc- 
tions. While  the  Milky  Way  is  the  narrowest  under  the 
foot  of  the  Cross,  the  region  of  minimum  brightness  (where 
there  is  the  greatest  paucity  of  stars  in  the  Galactic  zone)  is 
in  the  naighborhood  of  Monoceros  and  Perseus. 

The  magnificent  effulgence  of  the  Milky  Way  in  the  south- 
ern hemisphere  is  still  further  increased  by  the  circumstance 
that  between  the  star  r\  Argus,  which  has  become  so  cele- 
brated in  consequence  of  its  variability,  and  a  Crucis,  undei 
the  parallels  of  59°  and  60°  south  lat,  it  is  intersected  at 
an  angle  of  20°  by  the  remarkable  zone  of  very  large  and 
probably  very  proximate  stars,  to  which  belong  the  constella- 
tions Orion,  Canis  Major,  Scorpio,  Centaurus,  and  the  South- 
ern Cross.  The  direction  of  this  remarkable  zone  is  indi- 
cated by  a  great  circle  passing  through  e  Orionis  and  the 
foot  of  the  Cross.  The  picturesque  effect  of  the  Milky  Way, 
if  I  may  use  the  expression,  is  increased  in  both  hemispheres 
by  its  various  ramifications.  It  remains  undivided  for  about 
two  fifths  of  its  length.  According  to  Sir  John  Herschel's 
observations,  the  branches  separate  in  the  great  bifurcation 
at  a  Centauri,*  and  not  at  )3  Cent.,  as  given  in  our  maps  of 
the  stars,  or,  as  was  asserted  by  Ptolemy,t  in  the  constella- 
tion of  the  Altar  ;  they  reunite  again  in  Cygnus. 

In  order  to  obtain  a  general  insight  into  the  whole  course 
and  direction  of  the  Milky  Way  with  its  subdivisions,  we 
will  briefly  consider  its  parts,  following  the  order  of  their 
Right  Ascension.  Passing  through  y  and  e  Cassiopeiae,  the 
Milky  Way  sends  forth  toward  e  Persei  a  southern  branch, 
which  loses  itself  in  the  direction  of  the  Pleiades  and  Hyades. 
The  main  stream,  which  is  here  very  faint,  passes  on  through 
Auriga,  over  the  three  remarkable  stars  e,  £,  rj,  the  Hsedi  of 
that  constellation,  preceding  Capell  a,  between  the  feet  of  Gem- 
ini and  the  horns  of  the  Bull  (where  it  intersects  the  eclip- 

aware  of  its  having  risen  above  the  horizon,  though  he  should  not  be  at 
the  time  looking  at  the  heavens,  by  the  increase  of  general  illumination 
of  the  atmosphere,  resembling  the  effect  of  the  young  moon."  (See 
Piazzi  Smyth,  On  the  Orbit  of  a  Centauri,  in  the  Transact,  of  the  Royal 
Soc.  of  Edinburgh,  vol.  xvi.,  p.  445.) 

*  Outlines,  $  789.  791 ;   Observations  at  the  Cape,  $  325. 

t  Almagest,  lib.  viii.,  cap.  2  (t.  ii.,  p.  84,  90,  Halma).  Ptolemy's  de- 
scription is  admirable  in  some  parts,  especially  when  compared  with 
Aristotle's  treatment  of  the  subject  of  the  Milky  Way,  in  Meteor  (lib 
i.,  p.  29,  34,  according  to  Ideler's  edition). 


148  COSMOS. 

tic  nearly  in  the  solstitial  colure),  and  thence  over  Orion's 
club  to  the  neck  of  Monoceros,  intersecting  the  equinoctial 
(in  1800)  at  R.  A.  6h.  54m.  From  this  point  the  brightness 
considerably  increases.  At  the  stern  of  Argo  one  branch 
runs  southward  to  y  Argus,  where  it  terminates  abruptly. 
The  main  stream  is  continued  to  33°  S.  Decl.,  where,  after 
separating  in  a  fan-like  shape  (20°  in  breadth),  it  again 
breaks  off,  so  that  there  is  a  wide  gap  in  the  Milky  "Way  in 
the  line  from  y  to  A  Argus.  It  begins  again  in  a  similar 
fan-like  expansion,  but  contracts  at  the  hind  feet  of  the  Cen- 
taur and  before  its  entrance  into  the  Southern  Cross,  where 
it  is  at  its  narrowest  part,  and  is  only  3°  or  4°  in  width. 
Soon  after  this  the  Milky  Way  again  expands  into  a  bright 
and  broad  mass,  which  incloses  /3  Centauri  as  well  as  o  and 
ft  Crucis,  and  in  the  midst  of  which  lies  the  black  pear- 
shaped  coal-sack,  to  which  I  shall  more  specially  refer  in  the 
seventh  section.  In  this  remarkable  region,  somewhat  below 
the  coal-sack,  the  Milky  Way  approaches  nearest  to  the  South 
Pole. 

The  above-mentioned  bifurcation,  which  begins  at  a  Cen- 
tauri, extended,  according  to  older  views,  to  the  constellation 
Cygnus.  Passing  from  a  Centauri,  a  narrow  branch  runs 
northward  in  the  direction  of  the  constellation  Lupus,  where 
it  seems  gradually  lost ;  a  division  next  shows  itself  at  y 
Normse.  The  northern  branch  forms  irregular  outlines  till 
it  reaches  the  region  of  the  foot  of  Ophiuchus,  where  it  wholly 
disappears  ;  the  most  southern  branch  then  becomes  the 
main  stream,  and  passes  through  the  Altar  and  the  tail  of 
the  Scorpion,  in  the  direction  of  the  bow  of  Sagittarius, 
where  it  intersects  the  ecliptic  in  276°  long.  It  next  runs 
in  an  irregular  patchy  and  winding  stream  through  Aquila, 
Sagitta,  and  Vulpecula  up  to  Cygnus  ;  between  e,  a,  and  y, 
of  which  constellation  a  broad  dark  vacuity  appears,  which, 
as  Sir  John  Herschel  says,  is  not  unlike  the  southern  coal- 
sack,  and  serves  as  a  kind  of  center  for  the  divergence  of 
three  great  streams.*  One  of  these,  which  is  very  vivid  and 
conspicuous,  may  be  traced  running  backward,  as  it  were, 
through  j3  Cygni  and  f  Aquilae,  without,  however,  blending 
with  the  stream  already  noticed,  which  extends  to  the  foot 
of  Ophiuchus.  A  considerable  offset  or  protuberant  append- 
age is  also  thrown  off  by  the  northern  stream  from  the  head 

*  Outlines,  p.  531.  The  strikingly  dark  spot  between  a  and  y  Cas- 
siopeia; is  also  ascribed  to  the  contrast  with  the  brightness  by  which  it 
is  surrounded.  See  Struve,  Eludes  Stell.,  note  58. 


MILKY   WAY.  149 

of  Cepheus,  and  therefore  near  Cassiopeia  (from  which  con- 
stellation we  began  our  description  of  the  Milky  Way),  to- 
ward Ursa  Minor  and  the  pole. 

From  the  extraordinary  advancement  which  the  applica- 
tion of  large  telescopes  has  gradually  effected  in  our  knowl 
edge  of  the  sidereal  contents  and  of  the  differences  in  the 
concentration  of  light  observable  in  individual  portions  of  the 
Milky  Way,  views  of  merely  optical  projection  have  been  re- 
placed by  others  referring  rather  to  physical  conformation. 
Thomas  Wright,  of  Durham,*  Kant,  Lambert,  and  at  first 
also  Sir  William  Herschel,  were  disposed  to  consider  the 
form  of  the  Wilky  Way,  and  the  apparent  accumulation  of 
the  stars  within  this  zone,  as  a  consequence  of  the  flattened 
form  and  unequal  dimensions  of  the  world-island  (starry 
stratum)  in  which  our  solar  system  is  included.  The  hy- 
pothesis of  the  uniform  magnitude  and  distribution  of  the 
fixed  stars  has  recently  been  attacked  on  many  sides.  The 
bold  and  gifted  investigator  of  the  heavens,  Wm.  Herschel, 
in  his  last  works,!  expressed  himself  strongly  in  favor  of  the 
assumption  of  an  annulus  of  stars ;  a  view  which  he  had 
contested  in  the  talented  treatise  he  composed  in  1784.  The 
most  recent  observations  have  favored  the  hypothesis  of  a 
system  of  separate  concentric  rings.  The  thickness  of  these 
rings  seems  very  unequal ;  and  the  different  strata,  whose 
combined  stronger  or  fainter  light  we  receive,  are  undoubt- 
edly situated  at  very  differentjiltitudes,  i.  e.,  at  very  unequal 
distances  from  us ;  but  the  relative  brightness  of  the  sep- 
arate stars  which  we  estimate  as  of  the  tenth  to  the  six- 
teenth magnitude,  can  not  be  regarded  as  affording  sufficient 
data  to  enable  us  in  a  satisfactory  manner  to  deduce  numer- 
ically from  them  the  radius  of  their  spheres  of  distances.^ 

In  many  parts  of  the  Milky  Way,  the  space-penetrating 
power  of  instruments  is  sufficient  to  resolve  whole  star- 
clouds,  and  to  show  the  separate  luminous  points  projected 
on  the  dark,  starless  ground  of  the  heavens.  We  here  act- 

*  De  Morgan  has  given  an  extract  of  the  extremely  rare  work  of 
Thomas  Wright  of  Durham  (  Theory  of  the  Universe,  London,  1750),  p 
241  in  the  Philot.  Magazine,  ser.  iii.,  No.  32.  Thomas  Wright,  to  whose 
researches  the  attention  of  astronomers  has  been  so  permanently  di 
reeled  since  the  beginning  of  the  present  century,  through  the  ingen 
ions  speculations  of  Kant  and  William  Herschel,  observed  only  with  a 
reflector  of  one  foot  focal  length. 

t  Pfaff,  in  Will.  HertchePi  sdmmtl.  Schriften,  bd.  i.  (1826),  a.  78-8l ; 
Struve,  Etvdet  Stell.,  p.  35-44. 

$  Encke,  in  Schumacher's  Attr.  Nochr.,  No.  622,  1847  «  341-34C 


150  COSMOS. 

ually  look  through  as  into  free  space.  "  It  leads  us,"  says 
Sir  John  Herschel,  "  irresistibly  to  the  conclusion  that  in 
these  regions  we  see  fairly  through  the  starry  stratum."* 
In  other  regions  we  see,  as  it  were,  through  openings  and 
fissures,  remote  world-islands,  or  outhranching  portions  of  the 
annular  system  ;  in  other  parts,  again,  the  Milky  Way  has 
hitherto  been,  fathomless,  even  with  the  forty-feet  telescope. f 
Investigations  on  the  different  intensity  of  light  in  the  Milky 
Way,  as  well  as  on  the  magnitudes  of  the  stars,  which  regu- 
larly increase  in  number  from  the  galactic  poles  to  the  circle 
itself  (an  increase  especially  observable  for  30°  on  either  side 
of  the  Milky  Way  in  stars  below  the  eleventh  magnitude,  J 
and  therefore  in  |^ths  of  all  the  stars),  have  led  the  most 
recent  investigator  of  the  southern  hemisphere  to  remarkable 
views  and  probable  results  in  reference  to  the  form  of  the 
galactic  annular  system,  and  what  has  been  boldly  called 
the  sun's  place  in  the  world-island  to  which  this  annular 
system  belongs.  The  place  assigned  to  the  sun  is  eccentric, 
and  probably  near  a  point  where  the  stratum  bifurcates  or 
spreads  itself  out  into  two  sheets, §  in  one  of  those  desert  re- 
gions lying  nearer  to  the  Southern  Cross  than  to  the  oppo- 
site node  of  the  Milky  Way.ll  "The  depth  at  which  our 
system  is  plunged  in  the  sidereal  stratum  constituting  the 
galaxy,  reckoning  from  the  southern  surface  or  limit  of  that 

*  Outlines,  p.  536,  537,  where  we  find  the  following  words  on  the 
same  subject :  "  In  such  cases  it  is  equally  impossible  not  to  perceive 
that  we  are  looking  through  a  sheet  of  stars  nearly  of  a  size,  and  of 
no  great  thickness  compared  with  the  distance  which  separates  them 
from  us." 

t  Struve,  Etudes  Stell.,  p.  63.  Sometimes  the  largest  instruments 
reach  a  portion  of  the  heavens,  in  which  the  existence  of  a  starry  stra- 
tum, shining  at  a  remote  distance,  is  only  announced  by  "  a  uniform 
dotting  or  stippling  of  the  field  of  view."  See,  in  Observations  at  the 
Cape,  p.  390,  the  section  "  On  some  indications  of  very  remote  tele- 
scopic branches  of  the  Milky  Way,  or  of  an  independent  sidereal  sys- 
tem or  systems  bearing  a  resemblance  to  such  branches." 

t  Observations  at  the  Cape,  §  314. 

$  Sir  William  Herschel,  in  the  Philos.  Transact,  for  1785,  p.  21 ;  Sir 
John  Herschel,  Observations  at  the  Cape,  §  293.  Compare  also  Struve, 
Descr.  de  I' Observatoire  de  Poulkova,  1845,  p.  267-271. 

||  "  I  think,"  says  Sir  John  Herschel,  "  it  is  impossible  to  view  this 
splendid  zone  from  a  Centauri  to  the  Cross  without  an  impression 
amounting  almost  to  conviction  that  the  Milky  Way  is  not  a  mere  stra- 
tum, but  annular ;  or,  at  least,  that  our  system  is  placed  within  one  of 
the  poorer  or  almost  vacant  parts  of  its  general  mass,  and  that  eccen- 
trically, so  as  to  be  much  nearer  to  the  region  about  the  Cross  than  to 
that  diametrically  opposite  to  it."  (Mary  Somerville,  On  the  Connec- 
*ion  of  the  Physical  Sciences,  1846,  p.  419.) 


NEW  STARS.  151 

stratum,  is  about  equal  to  that  distance  which,  on  a  general 
average,  corresponds  to  the  light  of  a  star  of  the  ninth  or 
tenth  magnitude,  and  certainly  does  not  exceed  that  corre 
spending  to  the  eleventh."*  Where,  from  the  peculiar  nature 
of  individual  problems,  measurements  and  the  direct  evi- 
dence of  the  senses  fail,  we  see  but  dimly  those  results  which 
intellectual  contemplation,  urged  forward  by  an  intuitive  im- 
pulse, is  ever  striving  to  attain. 


IV. 

NEW  STARS  AND  STARS  THAT  HAVE  VANISHED.— VARIABLE  STARS, 
WHOSE  RECURRING  PERIODS  HAVE  BEEN  DETERMINED.— VARIA- 
TIONS IN  THE  INTENSITY  OF  THE  LIGHT  OF  STARS  WHOSE  PERI- 
ODICITY IS  AS  YET  UNINVESTIGATED. 

NEW  STARS. — The  appearance  of  hitherto  unseen  stars  in 
the  vault  of  heaven,  especially  the  sudden  appearance  of 
strongly-scintillating  stars  of  the  first  magnitude,  is  an  oc- 
currence in  the  realms  of  space  which  has  ever  excited  as- 
tonishment. This  astonishment  is  the  greater,  in  proportion 
as  such  an  event  as  the  sudden  manifestation  of  what  was 
before  invisible,  but  which  nevertheless  is  supposed  to  have 
previously  existed,  is  one  of  the  very  rarest  phenomena  in 
nature.  While,  in  the  three  centuries  from  1500  to  1800, 
as  many  as  forty-two  comets,  visible  to  the  naked  eye,  have 
appeared  to  the  inhabitants  of  the  northern  hemisphere—, 
on  an  average,  fourteen  in  every  hundred  years — only  eight 
new  stars  have  been  observed  throughout  the  same  period. 
The  rarity  of  the  latter  becomes  still  more  striking  when, 
we  extend  our  consideration  to  yet  longer  periods.  From 
the  completion  of  the  Alphonsine  Tables,  an  important  epoch 
in  the  history  of  astronomy,  down  to  the  time  of  William 
Herschel — that  is,  from  1252  to  1800 — the  number  of  visi- 
ble comets  is  estimated  at  about  sixty-three,  while  that  of 
new  stars  does  not  amount  to  more  than  nine.  Consequent- 
ly, for  the  period  during  which,  in  the  civilized  countries  of 
Europe,  we  may  depend  on  possessing  a  tolerably  correct 
enumeration  of  both,  the  proportion  of  new  stars  to  comets 
visible  to  the  naked  eye  is  as  one  to  seven.  We  shall  pres- 
ently show  that  if  from  the  tailless  comets  we  separate  the 
new  stars  which,  according  to  the  records  of  Ma-tuan-lin, 
*  Observations  at  the  Cape,  $  315. 


152  COSMOS. 

have  been  observed  in  China,  and  go  back  to  the  middle  o" 
the  second  century  before  the  Christian  era,  that  for  about 
2000  years  scarcely  more  than  twenty  or  twenty-two  of  such 
phenomena  can  be  adduced  with  certainty. 

Before  I  proceed  to  general  considerations,  it  seems  not 
inappropriate  to  quote  the  narrative  of  an  eye-witness,  and, 
by  dwelling  on  a  particular  instance,  to  depict  the  vividness 
of  the  impression  produced  by  the  sight  of  a  new  star.  "  On 
my  return  to  the  Danish  islands  from  my  travels  in  Germa- 
ny," says  Tycho  Brahe,  "  I  resided  for  some  time  with  my 
uncle,  Steno  Bille  (ut  aulicse  vitae  fastidium  lenirem),  in  the 
old  and  pleasantly  situated  monastery  of  Herritzwadt ;  and 
here  I  made  it  a  practice  not  to  leave  my  chemical  labora- 
tory until  the  evening.  Raising  my  eyes,  as  usual,  during 
one  of  my  walks,  to  the  well-known  vault  of  heaven,  I  ob- 
served, with  indescribable  astonishment,  near  the  zenith,  in 
Cassiopeia,  a  radiant  fixed  star,  of  a  magnitude  never  be- 
fore seen.  In  my  amazement,  I  doubted  the  evidence  of  my 
senses.  However,  to  convince  myself  that  it  was  no  illusion, 
and  to  have  the  testimony  of  others,  I  summoned  my  assist- 
ants from  the  laboratory,  and  inquired  of  them,  and  of  all 
the  country  people  that  passed  by,  if  they  also  observed  the 
star  that  had  thus  suddenly  burst  forth.  I  subsequently 
heard  that,  in  Germany,  wagoners  and  other  common  peo- 
ple first  called  the  attention  of  astronomers  to  this  great  phe- 
nomenon in  the  heavens — a  circumstance  which,  as  in  the 
case  of  non-predicted  comets,  furnished  fresh  occasion  for  the 
usual  raillery  at  the  expense  of  the  learned. 

"  This  new  star,"  Tycho  Brahe  continues,  "  I  found  to  be 
without  a  tail,  not  surrounded  by  any  nebula,  and  perfectly 
like  all  other  fixed  stars,  with  the  exception  that  it  scintil- 
lated more  strongly  than  stars  of  the  first  magnitude.  Its 
brightness  was  greater  than  that  of  Sirius,  a  Lyrse,  or  Jupi- 
ter. For  splendor,  it  was  only  comparable  to  Venus  when 
nearest  to  the  earth  (that  is,  when  only  a  quarter  of  her 
disk  is  illuminated).  Those  gifted  with  keen  sight  could, 
when  the  air  was  clear,  discern  the  new  star  in  the  daytime, 
and  even  at  noon.  At  night,  when  the  sky  was  overcast,  so 
that  all  other  stars  were  hidden,  it  was  often  visible  through 
the  clouds,  if  they  were  not  very  dense  (nubes  non  admo- 
dum  densas).  Its  distances  from  the  nearest  stars  of  Cassi- 
opeia, which,  throughout  the  whole  of  the  following  year,  I 
measured  with  great  care,  convinced  me  of  its  perfect  immo- 
bility. Already,  in  December,  1572,  its  brilliancy  began  to 


NiJW    STARS.  153 

diminish,  and  the  star  gradually  resettled  Jupiter ;  but  by 
January,  1573,  it  had  become  less  bright  than  that  planet. 
Successive  photometric  estimates  gave  the  following  results  : 
for  February  and  March,  equality  with  stars  of  the  first  mag- 
nitude (stellarum  affixarum  primi  honoris — for  Tycho  Brahe 
seems  to  have  disliked  using  Manilius's  expression  of  stellse 
fixae) ;  for  April  and  May,  with  stars  of  the  second  magni- 
tude ;  for  July  and  August,  with  those  of  the  third  ;  for  Oc- 
tober and  November,  those  of  the  fourth  magnitude.  To- 
ward the  month  of  November,  the  new  star  was  not  bright- 
er than  the  eleventh  in  the  lower  part  of  Cassiopeia's  chair. 
The  transition  to  the  fifth  and  sixth  magnitude  took  place 
between  December,  1573,  and  February,  1574.  In  the  fol- 
lowing month  the  new  star  disappeared,  and,  after  having 
shone  seventeen  months,  was  no  longer  discernible  to  the 
naked  eye."  (The  telescope  was  not  invented  until  thirty 
seven  years  afterward.) 

The  gradual  diminution  of  the  star's  luminosity  was,  more- 
over, invariably  regular ;  it  was  not  (as  is  the  case  in  the 
present  day  with  77  Argus,  though  indeed  that  is  not  to  be 
called  a  new  star)  interrupted  by  several  periods  of  rekind- 
ling or  by  increased  intensity  of  light.  Its  color  also  changed 
with  its  brightness  (a  fact  which  subsequently  gave  rise  to 
many  erroneous  conclusions  as  to  the  velocity  of  colored  rays 
in  their  passage  through  space).  At  its  first  appearance,  as 
long  as  it  had  the  brilliancy  of  Venus  and  Jupiter,  it  was 
for  two  months  white,  and  then  it  passed  through  yellow 
into  red.  In  the  spring  of  1573,  Tycho  Brahe  compared  it 
to  Mars ;  afterward  he  thought  that  it  nearly  resembled  Be- 
telgeux,  the  star  in  the  right  shoulder  of  Orion.  Its  color, 
for  the  most  part,  was  like  the  red  tint  of  Aldebaran.  In 
the  spring  of  1573,  and  especially  in  May,  its  white  color  re- 
turned (albedinem  quandam  sublividam  induebat,  qualis  Sa- 
turni  stellse  subesse  videtur).  So  it  remained  in  January, 
1574  ;  being,  up  to  the  time  of  its  entire  disappearance  in 
the  month  of  March,  1574,  of  the  fifth  magnitude,  and  white, 
but  of  a  duller  whiteness,  and  exhibiting  a  remarkably  strong 
scintillation  in  proportion  to  its  faintness. 

The  circumstantial  minuteness  of  these  statements*  is  of 

*  De  admiranda  Nova  Stella,  anno  1572,  exorta  in,  Tychonis  Brahe 
AttronomicE  instauratce  Progymnatmata,  1603,  p.  298-304,  and  578.  In 
the  text  I  have  closely  followed  the  account  which  Tycho  Brahe  him- 
self gives.  The  very  doubtful  statement  (which  is,  however,  repeated 
in  several  astronomical  treatises)  that  his  attention  was  first  called  to 


154  COSMOS. 

itself  a  proof  of  the  interest  which  this  natural  phenomenon, 
could  not  fail  to  awaken,  by  calling  forth  many  important 
questions,  in  an  epoch  so  brilliant  in  the  history  of  astronomy. 
For  (notwithstanding  the  general  rarity  of  the  appearance  of 
new  stars)  similar  phenomena,  accidentally  crowded  togeth- 
er within  the  short  space  of  thirty-two  years,  were  thrice  re- 
peated within  the  observation  of  European  astronomers,  and 
consequently  served  to  heighten  the  excitement.  The  im- 
portance of  star  catalogues,  for  ascertaining  the  date  of  the 
sudden  appearance  of  any  star,  was  more  and  more  recog- 
nized ;  the  periodicity*  (their  reappearance  after  many  cen- 
turies) was  discussed  ;  and  Tycho  Brahe  himself  boldly  ad- 
vanced a  theory  of  the  process  by  which  stars  might  be 
formed  and  molded  out  of  cosmical  vapor,  which  presents 
many  points  of  resemblance  to  that  of  the  great  William 
Herschel.  He  was  of  opinion  that  the  vapory  celestial  mat- 
ter, which  becomes  luminous  as  it  condenses,  conglomerates 
into  fixed  stars :  "  Coeli  materiam  tenuissimam,  ubique  nostro 
visui  et  planetarum  circuitibus  perviam,  in  unum  globum  con- 
densatam,  stellam  effingere."  This  celestial  matter,  which 
is  universally  dispersed  through  space,  has  already  attained 
to  a  certain  degree  of  condensation  in  the  Milky  Way,  which 
glimmers  with  a  soft  silvery  brightness.  Accordingly,  the 
place  of  the  new  star,  as  well  as  of  those  which  became  sud- 
denly visible  in  945  and  1264,  was  on  the  very  edge  of  the 
Milky  Way  (quo  factum  est  quod  nova  stella  in  ipso  galaxise 
margine  constiterit).  Indeed,  some  went  so  far  as  to  believe 
that  they  could  discern  the  very  spot  (the  opening  or  hiatus) 
whence  the  nebulous  celestial  matter  had  been  drawn  from 
the  Milky  Way.f  All  this  reminds  one  of  the  theories  of 

the  phenomenon  of  the  new  star  by  a  concourse  of  country  people, 
need  not,  therefore,  be  here  noticed. 

*  Cardanus,  in  his  controversy  with  Tycho  Brahe,  went  back  to  the 
star  of  the  Magi,  which,  as  he  pretended,  was  identical  with  the  star 
of  1572.  Ideler,  arguing  from  his  own  calculations  of  the  conjunctions 
of  Saturn  with  Jupiter,  and  from  similar  conjectures  advanced  by  Kep- 
ler on  the  appearance  of  the  new  star  in  Ophiucus  in  1604,  supposes 
that  the  star  of  the  Magi,  through  a  confusion  of  atnrjp  with  uarpnv, 
which  is  so  frequent,  was  not  a  single  great  star,  but  a  remarkable  con- 
junction of  stars — the  close  approximation  of  two  brightly-shining  plan- 
ets at  a  distance  of  less  than  a  diameter  of  the  moon. —  Tychonis  Pro- 
gymnasmata,  p.  324-330;  contrast  with  Ideler,  Handbuch  der  Malhe- 
matischen  nnd  Technischen  Chronologic,  bd.  ii.,  s.  399-407. 

t  Progymn.,  p.  324-330.  Tycho  Brahe,  in  his  theory  of  the  forma- 
tion of  new  stars  from  the  Cosmical  vapor  of  the  Milky  Way,  builds 
much  on  the  remarkable  passages  of  Aristotle  on  the  connection  of  the 


TEMPORARY    STARS. 


155 


transition  of  the  cosmical  vapor  into  clusters  of  stars,  of  an 
agglomerative  force,  of  a  concentration  to  a  central  nucleus, 
and  of  hypotheses  of  a  gradual  formation  of  solid  bodies  out 
of  a  vaporous  fluid — views  which  were  generally  received  in 
the  beginning  of  the  nineteenth  century,  but  which  at  pres- 
ent, owing  to  the  ever-changing  fluctuations  in  the  world  of 
thought,  are  in  many  respects  exposed  to  new  doubts. 

Among  newly-appeared  temporary  stars,  the  following 
(though  with  variable  degrees  of  certainty)  may  be  reckoned. 
I  have  arranged  them  according  to  the  order  in  which  they 
respectively  appeared. 


(a)      134  B.C. 

in  Scorpio. 

(b)      123  A.D. 

....   in  Ophiuchus. 

(c)       173    " 

....   in  Centaurus 

(d)     369    " 

7 

(e)      386    " 

....   in  Sagittarius. 

[f)    389    " 

.   in  Aquila. 

(s\     393    " 

in  Scorpio. 

\O  / 

ft)      827    " 

in  Scorpio. 

(i)       945    « 

....  between  Cepheus  and  Cassiopeia. 

A)    1012    " 

in  Aries. 

Z)     1203 

' 

in  Scorpio. 

m)  1230 

• 

in  Ophiuchus. 

n)    1264 

• 

between  Cepheus  and  Cassiopeia. 

(o)    1572 

1 

in  Cassiopeia. 

(p)  1578 

• 

(o)    1584 

' 

in  Scorpio. 

r)    1600 

' 

in  Cygnus. 

s)    1604 
t)     1609 

' 

in  Ophiuchus. 

u)    1670 

• 

in  Vulpes. 

v)    1848     ' 

in  Ophiuchus. 

EXPLANATORY  REMARKS. 

(<z)  This  star  first  appeared  in  July,  134  years  before  our  era.  We 
have  taken  it  from  the  Chinese  Records  of  Ma-tuan-lin,  for  the  transla- 
tion of  which  we  are  indebted  to  the  learned  linguist  Edward  Biot 
(  Connaistance  des  Temps  pour  Van  1846,  p.  6 1).  Its  place  was  between 
P  and  p  of  Scorpio.  Among  the  extraordinary  foreign-looking  stars  of 
these  records,  called  also  guest-stars  (etoiles  hdtes,  "  Ke-sing,"  strangers 
of  a  singular  aspect),  which  are  distinguished  by  the  observers  from 
comets  with  tails,  fixed  new  stars  and  advancing  tailless  comets  are  cer- 
tainly sometimes  mixed  up.  But  in  the  record  of  their  motion  (Ke-sing 

tails  of  comets  (the  vapory  radiation  from  their  nuclei)  with  the  galaxy 
to  which  I  have  already  alluded.     (Cotmos,  vol.  i.,  p.  103.) 


156  COSMOS. 

of  1092,  1181,  and  1458),  and  in  the  absence  of  any  si  ch  record,  as  also 
in  the  occasional  addition,  "  the  Ke-sing  dissolved"  (disappeared),  there 
is  contained,  if  not  an  infallible,  yet  a  very  important  criterion.  Besides, 
we  must  bear  in  mind  that  the  light  of  the  nucleus  of  all  comets,  wheth- 
er with  or  without  tails,  is  dull,  never  scintillates,  and  exhibits  only  a 
mild  radiance,  while  the  luminous  intensity  of  what  the  Chinese  call 
extraordinary  (stranger)  stars  has  been  compared  to  that  of  Venus — a 
circumstance  totally  at  variance  with  the  nature  of  .comets  in  general, 
and  especially  of  those  without  tails.  The  star  which  appeared  in  134 
B.C.,  under  the  old  Han  dynasty,  may,  as  Sir  John  Herschel  remarks, 
have  been  the  new  star  of  Hipparchus,  which,  according  to  the  state- 
ment of  Pliny,  induced  him  to  commence  his  catalogue  of  the  stars. 
Delambre  twice  calls  this  statement  a  fiction,  "  une  historiette."  (Hist, 
de  VAstr.  Anc.,  torn,  i.,  p.  290;  and  Hist,  de  VAstr.  Mod.,  torn,  i.,  p.  186.) 
Since,  according  to  the  express  statement  of  Ptolemy  (Almag.,  vii.,  p.  2, 
13,  Halmd),  the  catalogue  of  Hipparchus  belongs  to  the  year  128  B.C., 
and  Hipparchus  (as  I  have  already  remarked  elsewhere)  carried  on  his 
observations  in  Rhodes  (and  perhaps  also  in  Alexandria)  from  162  to 
127  B.C.,  there  is  nothing  irreconcilable  with  this  conjecture.  It  is  very 
probable  that  the  great  Nicean  astronomer  had  pursued  his  observations 
For  a  considerable  period  before  he  conceived  the  idea  of  forming  a  reg- 
ular catalogue.  The  words  of  Pliny,  "  suo  sevo  genita,"  apply  to  the 
whole  term  of  his  life.  After  the  appearance  of  Tycho  Brahe's  star  in 
1572,  it  was  much  disputed  whether  the  star  of  Hipparchus  ought  to  be 
classed  among  new  stars,  or  comets  without  tails.  Tycho  Brahe  himself 
was  of  the  former  opinion  (Progymn.,  p.  319-325).  The  words  "  ejus- 
que  motn  addubitationem  adcluctus"  may  undoubtedly  lead  to  the  sup- 
position of  a  faint,  or  altogether  tailless  comet;  but  Pliny's  rhetorical 
style  admitted  of  such  vagueness  of  expression. 

(b)  A  Chinese  observation.  It  appeared  in  December,  A.D.  123, 
between  a  Herculis  and  a  Ophiuchi.  Ed.  Biot,  from  Ma-tuan-lin.  (It 
is  also  asserted  that  a  new  star  appeared  in  the  reign  of  Hadrian,  about 
A.D.  130.) 

(r)  A  singular  and  very  large  star.  This  also  is  taken  from  Ma-tuan- 
lin,  as  well  as  the  three  following  ones. 

Jt  appeared  on  the  10th  of  December,  173,  between  a  and  /?  Centauri 
and  at  the  end  of  eight  months  disappeared,  after  exhibiting  the  five 
colors  one  after  another.  "  Successivement"  is  the  term  employed  by 
Ed.  Biot  in  his  translation.  Such  an  expression  would  almost  tend  to 
suggest  a  series  of  colors  similar  to  those  in  the  above-described  star 
of  Tycho  Brahe ;  but  Sir  John  Herschel  more  correctly  takes  it  to  mean 
a  colored  scintillation  (Ozttlines,  p.  563),  and  Arago  interprets  in  the  same 
way  a  nearly  similar  expression  employed  by  Kepler  when  speaking 
of  the  new  star  (1604)  in  Ophiuchus.  (Annuaire  pour  1842,  p.  347.) 

(d)  This  star  was  seen  from  March  to  August,  369. 

(e)  Between  A  and  <j>  Sagittarii.    In  the  Chinese  Record  it  is  expressly 
observed,  "  where  the  star  remained  (i.  e.,  without  movement)  from 
April  to  July,  386. 

(/)  A  new  star,  close  to  a  Aquilso.  In  the  year  389,  in  the  reign  of 
the  Emperor  Honorius,  it  shone  forth  with  the  brilliancy  of  Venus,  ac- 
cording to  the  statement  of  Cuspinianus,  who  had  himself  seen  it.  It 
totally  disappeared  in  about  three  weeks.* 

*  Other  accounts  place  the  appearance  in  the  year  388  or  398 
Jacques  Cassini,  Element  d'Astronomie,  1740  (Etottes  Nouvelles),  p.  59. 


TEMPORARY    STARS.  157 

(g)  March,  393.  This  star  was  also  in  Scorpio,  in  the  tail  of  that 
coustellation.  From  the  Records  of  Ma-tuan-lin. 

(h)  The  precise  year  (827)  is  doubtful.  It  may  with  more  certainty 
be  assigned  to  the  first  half  of  the  ninth  century,  when,  in  the  reign  of 
Calif  Al-Mamun,  the  two  famous  Arabian  astronomers,  Haly  and  Gia- 
far  Ben  Mohammed  Albumazar,  observed  at  Babylon  a  new  star,  whose 
light,  according  to  their  report,  "equaled  that  of  the  moon  in  her  quar- 
ters." This  natural  phenomenon  likewise  occurred  in  Scorpio.  The 
atar  disappeared  after  a  period  of  four  months. 

(t)  The  appearance  of  this  star  (which  is  said  to  have  shone  forth  in 
the  year  945,  under  Otho  the  Great),  like  that  of  1264,  is  vouched  for 
solely  by  the  testimony  of  the  Bohemian  astronomer  Cyprianus  Leovi- 
tius,  who  asserts  that  he  derived  his  statements  concerning  it  from  a 
manuscript  chronicle.  He  also  calls  attention  to  the  fact  that  these  two 
phenomena  (that  in  945  and  that  in  1264)  took  place  between  the  con- 
stellations of  Cepheus  and  Cassiopeia,  close  to  the  Milky  Way,  and  near 
the  spot  where  Tycho  Brahe's  star  appeared  in  1572.  Tycho  Brahe 
(Progym.,  p.  331  and  709)  defends  the  credibility  of  Cyprianus  Leovi- 
tius  against  the  attacks  of  Pontanus  and  Camerarius,  who  conjectured 
that  the  statements  arose  from  a  confusion  of  new  stars  with  long-tailed 
comets. 

(&)  According  to  the  statement  of  Hepidannus,  the  monk  of  St.  Gall 
(who  died  A.D.  1088,  whose  annals  extend  from  the  year  A.D.  709  to 
1044),  a  new  star  of  unusual  magnitude,  and  of  a  brilliancy  that  dazzled 
the  eye  (oculos  verberans),  was,  for  three  months,  from  the  end  of  May 
in  the  year  1012,  to  be  seen  in  the  south,  in  the  constellation  of  Aries. 
In  a  most  singular  manner  it  appeared  to  vary  in  size,  and  occasionally 
it  could  not  be  seen  at  all.  "  Nova  stella  apparuit  insolitae  magnitudinis, 
aspectu  fulgurans  et  oculos  verberans  non  sine  terrore.  Qua?  mirum  in 
modum  aliquando  contractior,  aliquando  diffusior,  etiam  extinguebatur 
interdum.  Visa  est  autem  per  tres  menses  in  intimis  finibus  Austri,  ul- 
tra omnia  signa  qute  videntur  in  ccelo."  (See  Hepidanni,  Annales  bre- 
ves, in  Duchesne,  Histories  Francorum  Scriptores,  t.  iii.,  1641,  p.  477. 
Compare  also  Schnurrer,  Chronik  der  Seuchen,  th.  i.,  s.  201.)  To  the 
manuscript  made  use  of  by  Duchesne  and  Goldast,  which  assigns  the 
phenomenon  to  the  year  1012,  modern  historical  criticism  has,  howev- 
er, preferred  another  manuscript,  which,  as  compared  with  the  former, 
exhibits  many  deviations  in  the  dates,  throwing  them  six  years  back. 
Thus  it  places  the  appearance  of  this  star  in  1006.  (See  Annales  San- 
gallenses  majores,  in  Pertz,  Afonumenta  Germanise  historica  Scriptorum, 
t.  i.,  1826,  p.  81.)  Even  the  authenticity  of  the  writings  of  Hepidannus 
has  been  called  into  question  by  modern  critics.  The  singular  phenom- 
enon of  variability  has  been  termed  by  Chladni  the  conflagration  and 
extinction  of  a  fixed  star.  Hind  (Notices  of  the  Asfron.  Soc.,  vol.  viii., 
1848,  p.  156)  conjectures  that  this  star  of  Hepidannus  is  identical  with 
a  new  star,  which  is  recorded  in  Ma-tuan-lin,  as  having  been  seen  in 
China,  in  February,  1011,  between  a  and  <p  of  Sagittarius.  But  in  that 
case  there  must  be  an  error  in  Ma-tuan-lin,  not  only  in  the  statement  of 
the  year,  but  also  of  the  constellation  in  which  the  star  appeared. 

(A  Toward  the  end  of  July,  1203,  in  the  tail  of  Scorpio.  According 
to  the  Chinese  Record,  this  new  star  was  "of  a  bluish-white  color, 
without  luminous  vapor,  and  resembled  Saturn."  (Edouard  Biot,  in  the 
Connaissance  des  Temps  pour  1846,  p.  68.) 

(TO)  Another  Chinese  observation,  from  Ma-tuan-lin,  whose  astronom- 
ical records,  containing  an  accurate  account  of  the  positions  «f  comet* 


158  COSMOS. 

and  fixed  stars,  go  back  to  the  year  613  B.C.,  to  the  times  of  Thalea 
and  the  expedition  of  Golaeus  of  Samoa.  This  new  star  appeared  in  the 
middle  of  December,  1230,  between  Ophiuchus  and  the  Serpent.  It 
dissolved  toward  the  end  of  March,  1231. 

(»)  This  is  the  star  mentioned  by  the  Bohemian  astronomer,  Gypri- 
anus  Leovitius  (and  referred  to  under  the  ninth  star,  in  the  year  945). 
About  the  same  time  (July,  1264),  a  great  comet  appeared,  whose  tail 
swept  over  one  half  of  the  heavens,  and  which,  therefore,  could  not  be 
mistaken  for  a  new  star  suddenly  appearing  between  Cepheus  and  Gas- 
siopeia. 

(o)  This  is  Tycho  Brahe's  star  of  the  llth  of  November,  1572,  in  the 
Chair  of  Cassiopeia,  R.  A.  3°  26' ;  Decl.  63°  3'  (for  1800). 

(p)  February,  1578.  Taken  from  Ma-tuan-lin.  The  constellation  ia 
not  given,  but  the  intensity  and  radiation  of  the  light  must  have  been 
extraordinary,  since  the  Chinese  Record  appends  the  remark,  "  a  star 
as  large  as  the  sun !" 

(?)  On  the  1st  of  July,  1584,  not  far  from  TT  of  Scorpio ;  also  a  Chinese 
observation. 

(r)  According  to  Bayer,  the  star  34  of  Cygnus.  Wilhelm  Jansen,  the 
celebrated  geographer,  who  for  a  time  had  been  the  associate  of  Tycho 
Brahe  in  his  observations,  was  the  first,  as  an  inscription  on  his  celes- 
tial globe  testifies,  to  draw  attention  to  the  new  star  in  the  breast  of  the 
Swan,  near  the  beginning  of  the  neck.  Kepler,  who,  after  the  death 
of  Tycho  Brahe,  was  for  some  time  prevented  from  carrying  on  any 
observations,  both  by  his  travels  and  want  of  instruments,  did  not  ob- 
serve it  till  two  years  later,  and,  indeed  (what  is  the  more  surprising, 
since  the  star  was  of  the  third  magnitude),  then  first  heard  of  its  exist- 
ence. He  thus  writes :  "  Cum  mense  Maio,  anni  1602,  primum  litteris 
monerer  de  novo  Cygni  phffinomeno."  (Kepler,  De  Stella  Nova  tertii 


honoris  in  Cygno,  1606,  which  is  appended  to  the  work  De  Stella  Nova 
in  Serpent.,  p.  152,  154,  164,  and  167.)  In  Kepler's  treatise  it  is  no- 
where said  (as  we  often  find  asserted  in  modern  works)  that  this  star 


of  Cygnus  upon  its  first  appearance  was  of  the  first  magnitude.  Kep- 
ler even  calls  it  "  parva  Cygni  stella,"  and  speaks  of  it  throughout  as 
one  of  the  third  magnitude.  He  determines  its  position  in  R.  A.  300° 
46' ;  Decl.  36°  52'  (therefore  for  1800 :  R.  A.  302°  36' ;  Decl.  -f  37°  27'). 
The  star  decreased  in  brilliancy,  especially  after  the  year  1619,  and  van- 
ished in  1621.  Dominique  Cassini  (see  Jacques  Cassini,  Ellmens  d'Astr., 
p.  69)  saw  it,  in  1655,  again  attain  to  the  third  magnitude,  and  then  dis- 
appear. Hevelius  observed  it  again  in  November,  1665,  at  first  ex- 
tremely small,  then  larger,  but  never  attaining  to  the  third  magnitude. 
Between  1677  and  1682  it  decreased  to  the  sixth  magnitude,  and  as  such 
it  has  remained  in  the  heavens.  Sir  John  Herschel  classes  it  among  the 
variable  stars,  in  which  he  differs  from  Argelander. 

(«)  After  the  star  of  1572  in  Cassiopeia,  the  most  famous  of  the  new 
stars  is  that  of  1604  in  Ophiuchus  (R.  A.  259°  42' ;  and  S.  Decl.  21°  15', 
for  1800).  With  each  of  these  stars  a  great  name  is  associated.  The 
star  in  the  right  foot  of  Ophiuchus  was  originally  discovered,  on  the  1  Oth 
of  October,  1604,  not  by  Kepler  himself,  but  by  his  pupil,  the  Bohemian 
astronomer,  John  Bronowski.  It  was  larger  than  all  stars  of  the  first 
order,  greater  than  Jupiter  and  Saturn,  but  smaller  than  Venus.  Her- 
licias  asserts  that  he  had  previously  seen  it  on  the  27th  of  September. 
Its  brilliancy  was  less  than  that  of  the  new  star  discovered  by  Tycho 
Brahe  in  1572.  Moreover,  unlike  the  latter,  it  was  not  discernible  in 
the  daytime.  But  its  scintillation  was  considerably  greater,  and  espe- 


TEMPORARY    STARS.  159 

cially  excited  the  astonishment  of  all  who  saw  it.  As  scintillation  is 
always  accompanied  with  dispersion  of  color,  much  has  been  said  of 
its  colored  and  continually-changing  light.  Arago  (Annuaire pour  1834, 
p.  209-301,  and  Ann.  pour  1842,  p.  345-347)  has  already  called  atten- 
tion to  the  fact  that  the  star  of  Kepler  did  not  by  any  means,  like  that 
of  Tycho  Brahe,  assume,  at  certain  long  intervals,  different  colors,  such 
as  yellow,  red,  and  then  again  white.  Kepler  says  expressly  that  his 
star,  as  soon  as  it  rose  above  the  exhalations  of  the  earth,  was  white. 
When  he  speaks  of  the  colors  of  the  rainbow,  it  is  to  convey  a  clear 
idea  of  its  colored  scintillation.  His  words  are:  "  Exemplo  adamantis 
multanguli,  qui  solis  radios  inter  convertendum  ad  spectantium  oculos 
variabili  fulgore  revibraret,  colores  Iridis  (stella  nova  in  Ophiucho)  sue- 
sessive  vibratu  continue  reciprocabat."  (De  Nova  Stella  Serpent.,  p.  5 
and  125.)  In  the  beginning  of  January,  1605,  this  star  was  even  brighter 
than  Antares,  but  less  luminous  than  Arcturus.  By  the  end  of  March  in 
the  same  year  it  was  described  as  being  of  the  third  magnitude.  Its 
proximity  to  the  sun  prevented  all  observation  for  four  months.  Be- 
tween February  and  March,  1606,  it  totally  disappeared.  The  inaccu- 
rate statements  as  to  the  great  variations  in  the  position  of  the  new  star, 
advanced  by  Scipio  Claramontius  and  the  geographer  Blaew,  are  scarcely 
(as  Jacques  Cassini,  Elemens  d'Astr.,  p.  65,  long  since  observed)  deserv- 
ing of  notice,  since  they  have  been  refuted  by  Kepler's  more  trustworthy 
treatise.  The  Chinese  Record  of  Ma-tuan-lin  mentions  a  phenomenon 
which  exhibits  some  points  of  resemblance,  as  to  time  and  position,  with 
this  sudden  appearance  of  a  new  star  in  Ophiuchus.  On  the  30th  of 
September,  1604,  there  was  seen  in  China  a  reddish-yellow  ("  ball- 
like?")  star,  not  far  from  TT  of  Scorpio.  It  shone  in  the  southwest  till 
November  of  the  same  year,  when  it  became  invisible.  It  reappeared 
on  the  14th  of  January,  16t)5,  in  the  southeast;  but  its  light  became 
slightly  duller  by  March,  1606.  (Connaissance  des  Temps  pour  1846, 
p.  59.)  The  locality,  TT  of  the  Scorpion,  might  easily  be  confounded 
with  the  foot  of  Ophiuchus ;  but  the  expressions  southwest  and  south- 
east, its  reappearance,  and  the  circumstance  that  its  ultimate  total  dis 
appearance  is  not  mentioned,  leave  some  doubts  as  to  its  identity. 

(£)  This  also  is  a  new  star  of  considerable  magnitude,  and  seen  in  the 
southwest.  It  is  mentioned  in  Ma-tuau-lin.  No  further  particulars  are 
recorded. 

(M)  This  is  the  new  star  discovered  by  the  Carthusian  monk  Anthel- 
mus  on  the  20th  of  June,  1670,  in  the  head  of  Vulpes  (R.  A.  294°  27'; 
Decl.  26°  47'),  and  not  far  from  /?  Cygni.  At  its  first  appearance  it  was 
not  of  the  first,  but  merely  of  the  third  magnitude,  and  on  the  10th  of 
August  it  diminished  to  the  fifth.  It  disappeared  after  three  months, 
but  showed  itself  again  on  the  17th  of  March,  1671,  when  it  was  of  the 
fourth  magnitude.  Dominique  Cassini  observed  it  very  closely  in  April, 
1671,  and  found  its  brightness  very  variable.  The  new  star  is  reported 
to  have  regained  its  original  splendor  after  ten  months,  but  in  Februa- 
ry, 1672,  it  was  looked  for  in  vain.  It  did  not  reappear  until  the  29th 
of  March  in  the  same  year,  and  then  only  as  a  star  of  the  sixth  magni- 
tude ;  since  that  time  it  has  never  been  observed.  (Jacques  Cassini, 
Element  d'Astr.,  p.  69—71.)  These  phenomena  induced  Dominique 
Cassini  to  search  for  stars  never  before  seen  (by  him !).  He  main 
tained  that  he  had  discovered  fourteen  such  stars  of  the  fourth,  fifth, 
and  sixth  magnitudes  (eight  in  Cassiopeia,  two  ir  Eridanus,  and  four 
near  the  North  Pole).  From  the  absence  of  any  precise  data  as  to  their 
respective  positions,  and  especially  since,  like  those  said  to  have  been 


160  COSMOS. 

discovered  by  Maraldi  between  1694  and  1709,  their  existence  is  more 
than  questionable,  they  can  not  be  introduced  in  our  present  list. 
(Jacques  Cassini,  Elimens  tfAstron.,  p.  73-77  ;  Delambre,  Hist,  de 
VAstr.  Mod.,  t.  ii.,  p.  780.) 

(t?)  One  hundred  and  seventy-eight  years  elapsed  after  the  appear- 
ance of  the  new  star  in  Vulpes  without  a  similar  phenomenon  having 
occurred,  although  in  this  long  interval  the  heavens  were  most  care- 
fully explored,  and  its  stars  counted,  by  the  aid  of  a  more  diligent  use 
of  telescopes  and  by  comparison  with  more  correct  catalogues  of  the 
stars.  On  the  28.  h  of  April,  1848,  at  Mr.  Bishop's  private  observatory 
(South  Villa,  Regent's  Park),  Hind  made  the  important  discovery  of  a 
new  reddish-yellow  star  of  the  fifth  magnitude  in  Ophiuchus  (R.  A.  16° 
50'  59" ;  S.  Decl.  12°  39'  16",  for  1848).  In  the  case  of  no  other  new 
star  have  the  novelty  of  the  phenomenon  and  the  invariability  of  its  po- 
sition been  demonstrated  with  greater  precision.  At  the  present  time 
(1850)  it  is  scarcely  of  the  eleventh  magnitude,  and,  according  to  Lich 
tenberger's  accurate  observations,  it  will  most  likely  soon  disappear. 
(Notices  of  the  Astr.Soc.,vo\.  viii.,  p.  146  and  155-158.) 

The  above  list  of  new  stars,  which,  within  the  last  two 
thousand  years,  have  suddenly  appeared  and  again  disap- 
peared, is  probably  more  complete  than  any  before  given,  and 
may  justify  a  few  general  remarks.  We  may  distinguish  three 
classes :  new  stars  which  suddenly  shine  forth,  and  then,  after 
a  longer  or  shorter  time,  disappear  ;  stars  whose  brightness  is 
subject  to  a  periodical  variability,  which  has  been  already 
determined  ;  and  stars,  like  77  Argus*  which  suddenly  exhib- 
it an  unusual  increase  of  brilliancy,  the  variations  of  which 
are  still  undetermined.  All  these  phenomena  are,  most  prob- 
ably, intrinsically  related  to  each  other.  The  new  star  in 
Cygnus  (1600),  which,  after  its  total  disappearance  (at  least 
to  the  naked  eye),  again  appeared  and  continued  as  a  star  of 
the  sixth  magnitude,  leads  us  to  infer  the  affinity  of  the  two 
first  kinds  of  celestial  phenomena.  The  celebrated  star  dis- 
covered by  Tycho  Brahe  in  Cassiopeia  in  1572  was  consid- 
ered, even  while  it  was  still  shining,  to  be  identical  with  the 
new  star  of  945  and  1264.  The  period  of  300  years  which 
Goodricke  conjectured,  has  been  reduced  by  Keill  and  Pigott 
to  150  years.  The  partial  intervals  of  the  actual  phenom- 
ena, which  perhaps  are  not  very  numerically  accurate,  amount 
to  319  and  308  years.  Arago*  has  pointed  out  the  great 
improbability  that  Tycho  Brahe's  star  of  1572  belongs  to 
those  which  are  periodically  variable.  Nothing,  as  yet, 
seems  to  justify  us  in  regarding  all  new  stars  as  variable  in 
long  periods,  which  from  their  very  length  have  remained 
unknown  to  us.  If,  for  instance,  the  self-luminosity  of  all 
the  suns  of  the  firmament  is  the  result  of  an  electro-mag- 

*  Arago,  Annuaire  pour  1842,  p.  332. 


NEW    STARS  161 

netic  process  in  their  photospheres,  we  may  consider  this 
process  of  light  as  variable  in  many  ways,  without  assuming 
any  local  or  temporary  condensations  of  the  celestial  ether, 
or  any  intervention  of  the  so-called  cosmical  clouds.  It  may 
either  occur  only  once  or  recur  periodically,  and  either  regu- 
larly or  irregularly.  The  electrical  processes  of  light  on  our 
earth,  which  manifest  themselves  either  as  thunder-storms 
in  the  regions  of  the  air,  or  as  polar  effluxes,  together  with 
much  apparently  irregular  variation,  exhibit  nevertheless  a 
certain  periodicity  dependent  both  on  the  seasons  of  the  year 
and  the  hours  of  the  day  ;  and  this  fact  is,  indeed,  frequent- 
ly observed  in  the  formation  for  several  consecutive  days, 
during  perfectly  clear  weather,  of  a  small  mass  of  clouds  in 
particular  regions  of  the  sky,  as  is  proved  by  the  frequent 
failures  in  attempts  to  observe  the  culmination  of  stars. 

The  circumstance  that  almost  all  these  new  stars  burst 
forth  at  once  with  extreme  brilliancy  as  stars  of  the  first  mag- 
nitude, and  even  with  still  stronger  scintillation,  and  that 
they  do  not  appear,  at  least  to  the  naked  eye,  to  increase 
gradually  in  brightness,  is,  in  my  opinion,  a  singular  pecul- 
iarity, and  one  well  deserving  of  consideration.  Kepler*  at- 
tached such  weight  to  this  criterion,  that  he  refuted  the  idle 
pretension  of  Antonius  Laurentinus  Politianus  to  having  seen 
tiio  star  in  Ophiuchus  (1604)  before  Bronowski  simply  by 
the  circumstance  that  Laurentinus  had  said,  "  Apparuit  nova 
Stella  parva  et  postea  de  die  in  diem  crescendo  apparuit  lu- 
mine  non  multo  inferior  Venere,  superior  Jove."  There  are 
only  three  stars,  which  may  be  looked  upon  in  the  light  of 
exceptions,  that  did  not  shine  forth  at  once  as  of  the  first 
magnitude  ;  viz.,  the  star  which  appeared  in  Cygnus  in 
1600,  and  that  in  Vulpes  in  1670,  which  were  both  of  the 
third,  and  Hind's  ne  tar  in  Ophiuchus  in  1848,  which  is 
of  the  fifth  magnitude. 

It  is  much  to  be  regretted,  as  we  have  already  observed, 
that  after  the  invention  of  the  telescope  in  the  long  period 
of  178  years,  only  two  new  stars  have  been  seen,  whereas 
these  phenomena  have  sometimes  occurred  in  such  rapid  suc- 
cession, that  at  the  end  of  the  fourth  century  four  were  ob- 
served in  twenty-four  years  ;  in  the  thirteenth  century,  three 
in  sixty-one  years  ;  and  during  the  era  of  Tycho  Brahe  and 
Kepler,  at  the  end  of  the  sixteenth  and  beginning  of  the  sev- 
enteenth centuries,  no  less  than  six  were  observed  within  a 

*  Kepler,  De  Stella  Nova  in  pede  Serp.,  p.  3. 


162  COSMOS. 

period  of  thirty-seven  years.  Throughout  this  examination  I 
have  kept  in  view  the  Chinese  observations  of  extraordinary 
stars,  most  of  which,  according  to  the  opinion  of  the  most 
eminent  astronomers,  are  deserving  of  our  confidence.  Why 
it  is  that  of  the  new  stars  seen  in  Europe,  that  of  Kepler  in 
Ophiuchus  (1604)  is  in  all  probability  recorded  in  the  rec- 
ords of  Ma-tuan-lin,  while  that  of  Tycho  in  Cassiopeia  (1572) 
is  not  noticed,  I,  for  my  part,  am  as  little  able  to  explain  as 
I  am  to  account  for  the  fact  that  no  mention  was  made  in 
the  sixteenth  century,  among  European  astronomers,  of  the 
great  luminous  phenomenon  which  was  observed  in  China 
in  February,  1578.  The  difference  of  longitude  (1 14°)  could 
only,  HI  a  few  instances,  account  for  their  not  being  visible. 
Whoever  has  been  engaged  in  such  investigations,  must  be 
well  aware  that  the  want  of  record  either  of  political  events 
or  natural  phenomena,  either  upon  the  earth  or  in  the  heav- 
ens, is  not  invariably  a  proof  of  their  never  having  taken 
place  ;  and  on  comparing  together  the  three  different  cata- 
logues which  are  given  in  Ma-tuan-lin,  we  actually  find  com- 
ets (those,  for  instance,  of  1385  and  1495)  mentioned  in  one 
but  omitted  in  the  others. 

Even  the  earlier  astronomers  (Tycho  Brahe  and  Kepler), 
as  well  as  the  more  modern  (Sir  John  Herschel  and  Hind), 
have  called  attention  to  the  fact  that  the  great  majority  (four 
fifths,  I  make  it)  of  all  the  new  stars  described  both  in  Eu- 
rope and  China  have  appeared  in  the  neighborhood  of  or 
within  the  Milky  Way.  If  that  which  gives  so  mild  and 
nebulous  a  light  to  the  annular  starry  strata  of  the  Milky 
Way  is,  as  is  more  than  probable,  a  mere  aggregation  of 
small  telescopic  stars,  Tycho  Brahe's  hypothesis,  which  wo 
have  already  mentioned,  of  the  formation  of  new,  suddenly- 
shining  fixed  stars,  by  the  globular  condensation  of  celestial 
vapor,  falls  at  once  to  the  ground.  What  the  influence  of 
gravitation  may  be  among  the  crowded  strata  and  clusters 
of  stars,  supposing  them  to  revolve  round  certain  central  nu- 
clei, is  a  question  not  to  be  here  determined,  and  belongs  to 
the  mythical  part  of  Astrognosy.  Of  the  twenty-one  new 
stars  enumerated  in  the  above  list,  five  (those  of  134,  393, 
827,  1203,  and  158  1)  appeared  in  Scorpio,  three  in  Cassi- 
opeia and  Cepheus  (945,  1264,  1572),  and  four  in  Ophiu- 
chus (123,  1230,  1604,  1848).  Once,  however  (1012),  one 
was  seen  in  Aries  at  a  great  distance  from  the  Milky  Way 
(ths  star  seen  by  the  monk  of  St.  Gall).  Kepler  himself 
who,  however,  considers  as  a  new  star  that  described  by  Fa 


VANISHED  STARS.  163 

bricius  as  suddenly  shining  in  the  neck  of  Cetus  in  the  year 
1596,  and  as  disappearing  in  October  of  the  same  year,  like- 
wise advances  this  position  as  a  proof  to  the  contrary.  (Kep- 
ler, De  Stella  Nova  Serp.,  p.  112.)  Is  it  allowable  to  in- 
fer, from  the  frequent  lighting  up  of  such  stars  in  the  same 
constellations,  that  in  certain  regions  of  space — those,  name- 
ly, where  Cassiopeia  and  Scorpio  are  to  be  seen — the  condi- 
tions of  their  illuminations  are  favored  by  certain  local  re- 
lations ?  Do  such  stars  as  are  peculiarly  fitted  for  the  ex- 
plosive temporary  processes  of  light  especially  lie  in  those 
directions  ? 

The  stars  whose  luminosity  was  of  the  shortest  duration 
were  those  of  389,  827,  and  1012.  In  the  first  of  the  above- 
named  years,  the  luminosity  continued  only  for  three  weeks  ; 
in  the  second,  four  months ;  in  the  third,  three.  On  the 
other  hand,  Tycho  Brahe's  star  in  Cassiopeia  continued  to 
shine  for  seventeen  months ;  while  Kepler's  star  in  Cygnus 
(1600)  was  visible  fully  twenty-one  years  before  it  totally 
disappeared.  It  was  again  seen  in  1655,  and  still  of  the 
third  magnitude,  as  at  its  first  appearance,  and  afterward 
dwindled  down  to  the  sixth  magnitude,  without,  however 
(according  to  Argelander's  observations),  being  entitled  to 
rank  among  periodically  variable  stars. 

STARS  THAT  HAVE  DISAPPEARED.  —  The  observation  and 
enumeration  of  stars  that  have  disappeared  is  of  importance 
for  discovering  the  great  number  of  small  planets  which  prob- 
ably belong  to  our  solar  system.  Notwithstanding,  however, 
the  great  accuracy  of  the  catalogued  positions  of  telescopic 
fixed  stars  and  of  modern  star-maps,  the  certainty  of  convic- 
tion that  a  star  in  the  heavens  has  actually  disappeared  since 
a  certain  epoch  can  only  be  arrived  at  with  great  caution. 
Errors  of  actual  observation,  of  reduction,  and  of  the  press,* 

*  On  instances  of  stars  which  have  not  disappeared,  see  Argelander, 
in  Schumacher's  Astronom.  Nachr.,  No.  624,  e.  371.  To  adduce  an  ex- 
ample from  antiquity,  I  may  point  to  the  fact  that  the  carelessness  with 
which  Aratus  compiled  his  poetical  catalogue  of  the  stars  has  led  to  the 
often-renewed  question  whether  Vega  Lyrze  is  a  new  star,  or  one  which 
varies  in  long  periods.  For  instance,  Aratus  asserts  that  the  constella- 
tion of  Lyra  consists  wholly  of  small  stars.  It  is  singular  that  Hippar- 
chus,  in  his  Commentary,  does  not  notice  this  mistake,  especially  as  he 
censures  Aratus  for  his  statements  as  to  the  relative  intensity  of  light  in 
the  stars  of  Cassiopeia  and  Ophiuchus.  All  this,  however,  is  only  ac- 
cidental and  not  demonstrative  ;  for  when  Aratus  also  ascribes  to  Cyg- 
nus none  but  stars  "  of  moderate  brilliancy,"  Hipparchus  expressly  re- 
futes this  error,  and  adds  the  remark  that  the  bright  star  in  the  Swan 


164  COSMOS. 

often  disfigure  the  very  best  catalogues.  The  disappearance 
of  a  heavenly  body  from  the  place  in  which  it  had  before 
been  distinctly  seen,  may  be  the  result  of  its  own  nution  as 
much  as  of  any  such  diminution  of  its  photometric  process 
(whether  on  its  surface  or  in  its  photosphere),  as  would  ren- 
der the  waves  of  light  too  weak  to  excite  our  organs  of  sight. 
What  we  no  longer  see  is  not  necessarily  annihilated.  The 
idea  of  destruction  or  combustion,  as  applied  to  disappearing 
stars,  belongs  to  the  age  of  Tycho  Brahe.  Even  Pliny,  in 
the  fine  passage  where  he  is  speaking  of  Hipparchus,  makes 
i  a  question :  Stellae  an  obirent  nascerenturve  ?  The  ap- 
parent eternal  cosmical  alternation  of  existence  and  destruc- 
tion is  not  annihilation  ;  it  is  merely  the  transition  of  matter 
into  new  forms,  into  combinations  which  are  subject  to  new 
processes.  Dark  cosmical  bodies  may  by  a  renewed  process 
of  light  again  become  luminous. 

PERIODICALLY  VARIABLE  STARS. — Since  all  is  in  motion  in 
the  vault  of  heaven,  and  every  thing  is  variable  both  in  space 
and  time,  we  are  led  by  analogy  to  infer  that  as  the  fixed 
stars  universally  have  not  merely  an  apparent,  but  also  a 
proper  motion  of  their  own,  so  their  surfaces  or  luminous  at- 
mospheres are  generally  subject  to  those  changes  which  re- 
cur, in  the  great  majority,  in  extremely  long,  and,  therefore, 
unmeasured  and  probably  undeterminable  periods,  or  which, 
in  a  few,  occur  without  being  periodical,  as  it  were,  by  a 
sudden  revolution,  either  for  a  shorter  or  for  a  longer  time. 
The  latter  class  of  phenomena  (of  which  a  remarkable  in- 
stance is  furnished  in  our  own  days  by  a  large  star  in  Argo) 
will  not  be  here  discussed,  as  our  proper  subject  is  those  fixed 
stars  whose  periods  have  already  been  investigated  and  as- 
certained. It  is  of  importance  here  to  make  a  distinction 
between  three  great  sidereal  phenomena,  whose  connection 
has  not  as  yet  been  demonstrated  ;  namely,  variable  stars  of 
known  periodicity ;  the  instantaneous  lighting  up  in  the  heav- 
ens of  so-called  new  stars ;  and  sudden  changes  in  the  lu- 
minosity of  long-known  fixed  stars,  which  previously  shone 

(Deneb)  is  little  inferior  in  brilliancy  to  Lyra  (Vega  Lyra;).  Ptolemy 
classes  Vega  among  stars  of  the  first  magnitude,  and  in  the  Cataster 
isms  of  Eratosthenes  (cap.  25),  Vega  is  caEed  Tievnov  KOI  TiOfnrpnv.  Con 
sidering  the  many  inaccuracies  of  a  poet,  who  never  himself  observed 
the  stars,  one  is  not  much  disposed  to  give  credit  to  the  assertion  that  it 
was  only  between  the  years  272  and  127  B.C.,  i.  e.,  between  the  times 
of  Aratus  and  Hipparchus,  that  the  star  Vega  Lyrae  (Fidicula  of  Pliny, 
xviii.,  25)  became  a  star  of  the  first  magnitude. 


PERIODICAL  STARS.  165 

with  uniform  intensity.  We  shall  first  of  all  dwell  exclu- 
sively on  the  first  kind  of  variability  ;  of  this,  the  earliest  in- 
stance accurately  observed  is  furnished  (1638)  by  Mira,  a 
star  in  the  neck  of  Cetus.  The  East-Friesland  pastor,  David 
Fabricius  (the  father  of  the  discoverer  of  the  spots  on  the 
sun),  had  certainly  already  observed  this  star  on  the  13th  of 
August,  1596,  as  of  the  third  magnitude,  and  in  October  of 
the  same  year  he  saw  it  disappear.  But  it  was  not  until  for- 
ty-two years  afterward  that  the  alternating,  recurring  vari- 
ability of  its  light,  and  its  periodic  changes,  were  discovered 
by  the  Professor  Johann  Phocylides  Holwarda,  Professor  of 
Franeker.  This  discovery  was  further  followed  in  the  same 
century  by  that  of  two  other  variable  stars,  ft  Persei  (1669), 
described  by  Montanari,  and  %  Cygni  (1687),  by  Kirch. 

The  irregularities  which  have  been  noticed  in  the  periods, 
together  with  the  additional  number  of  stars  of  this  class 
which  have  been  discovered,  have,  since  the  beginning  of  the 
nineteenth  century,  awakened  the  most  lively  interest  in  this 
complicated  group  of  phenomena.  From  the  difficulty  of  the 
subject,  and  from  my  own  wish  to  be  able  to  set  down  in  the 
present  work  the  numerical  elements  of  this  variability  (as 
being  the  most  important  result  of  all  observations),  so  far  as 
in  the  present  state  of  the  science  they  have  been  ascertain- 
ed, I  have  availed  myself  of  the  friendly  aid  of  that  astrono- 
mer who  of  all  our  cotemporaries  has  devoted  himself  with 
the  greatest  diligence,  and  with  the  most  brilliant  success, 
to  the  study  of  the  periodically  varying  stars.  The  doubts 
and  questions  called  forth  by  my  own  labors  I  confidently 
laid  before  my  worthy  friend  Argelander,  the  director  of  the 
Observatory  at  Bonn,  and  it  is  to  his  manuscript  communi 
cations  that  I  am  solely  indebted  for  all  that  follows,  which 
for  the  most  part  has  never  before  been  published. 

The  greater  number  of  the  variable  stars,  although  not  all, 
are  of  a  red  or  reddish  color.  Thus,  for  instance,  besides  /3 
Persei  (Algol  in  the  head  of  Medusa),  /3  Lyrae  and  e  Aurigse 
have  also  a  white  light.  The  star  77  Aquilae  is  rather  yellow- 
ish ;  so  also,  in  a  still  less  degree,  is  £  Geminorum.  The  old 
assertion  that  some  variable  stars  (and  especially  Mira  Ceti) 
are  redder  when  their  brilliancy  is  on  the  wane  than  on  the 
increase,  seems  to  be  groundless.  Whether,  in  the  double 
star  a  Herculis  (in  which,  according  to  Sir  John  Herschel, 
the  greater  star  is  red,  but  according  to  Struve  yellow,  while 
its  companion  is  said  to  be  dark  blue),  the  small  companion, 
estimated  at  between  the  fifth  to  the  seventh  magnitude,  ia 


166  COSMOS. 

itself  also  variable,  appears  very  problematical.  Struve* 
himself  merely  says,  Suspicor  minorem  esse  variabilem, 
Variability  is  by  no  means  a  necessary  concomitant  of  red- 
ness. There  are  many  red  stars  :  some  of  them  very  red — 
as  Arcturus  and  Aldebaran — in  which,  however,  no  variabil- 
ity has  as  yet  been  discovered.  And  it  is  also  more  than 
doubtful  in  the  case  of  a  star  of  Cepheus  (No.  7582  of  the 
catalogue  of  the  British  Association),  which,  on  account  of 
its  extreme  redness,  has  been  called  by  William  Herschel 
the  Garnet  Star  (1782). 

It  would  be  difficult  to  indicate  the  number  of  periodically 
variable  stars  for  the  reason  that  the  periods  already  determ- 
ined are  all  irregular  and  uncertain,  even  if  there  were  no 
other  reasons.  The  two  variable  stars  of  Pegasus,  as  well 
as  a  Hydra,  s  Aurigse,  and  a  Cassiopeise,  have  not  the  cer- 
tainty that  belongs  to  Mira  Ceti,  Algol,  and  6  Cephei.  In 
inserting  them,  therefore,  in  a  table,  much  will  depend  on 
the  degree  of  certainty  we  are  disposed  to  be  content  with. 
Argelander,  as  will  be  seen  from  the  table  at  the  close  of 
this  investigation,  reckons  the  number  of  satisfactorily  de- 
termined periods  at  only  twenty-four.t 

The  phenomenon  of  variability  is  found  not  only  both  in 
red  and  in  some  white  stars,  but  also  in  stars  of  the  most  di- 
versified magnitude  ;  as,  for  example,  in  a  star  of  the  first 
magnitude,  a  Orionis  ;  by  Mira  Ceti,  a  Hydra,  a  Cassiopeiae, 
and  (3  Pegasi,  of  the  second  magnitude  ;  ft  Persei,  of  the  2'3d 
magnitude  ;  and  in  77  Aquilse,  and  (3  Lyrse,  of  the  3'4th  mag- 
nitude. There  are  also  variable  stars,  and,  indeed,  in  far 
greater  numbers,  of  the  sixth  to  the  ninth  magnitude,  such 
as  the  variabiles  Coronae,  Virginis,  Cancri,  et  Aquarii.  The 
star  %  Cygni  likewise  presents  very  great  fluctuations  at  its 
maximum. 

*  Compare  Madler,  Astr.,  s.  438,  note  12,  with  Struve,  Stellarum, 
compos.  Mensurce  Microm.,  p.  97  and  98,  star  2140.  "I  believe,"  says 
Argelander,  "it  is  extremely  difficult  with  a  telescope  having  a  great 
power  of  illumination  to  estimate  rightly  the  brightness  of  two  such 
different  stars  as  the  two  components  of  a  Herculis.  My  experience 
is  strongly  against  the  variability  of  the  companion;  or,  during  my 
many  observations  in  the  daytime  with  the  telescopes  of  the  meridian 
circles  of  Abo,  Helsingfors,  and  Bonn,  I  have  never  seen  a  Herculis 
single,  which  would  assuredly  have  been  the  case  if  the  companion  at 
its  minimum  were  of  the  seventh  magnitude.  I  believe  the  latter  to 
be  constant,  and  of  the  fifth  or  5-6th  magnitude." 

t  Madler's  Table  (Astron.,  s.  435)  contains  eighteen  stars,  with  widely 
differing  numerical  elements.  Sir  John  Herschel  enumerates  more  than 
forty-five,  including  those  mentioned  in  the  notes. — Outlines,  §  819-826. 


VARIABLE   STARS.  167 

That  the  periods  of  the  variable  stars  are  very  irregular 
has.  been,  long  known  ;  but  that  this  variability,  with  all  its 
apparent  irregularity,  is  subject  to  certain  definite  laws,  was 
first  established  by  Argelander.  This  he  hopes  to  be  able 
to  demonstrate  in  a  longer  and  independent  treatise  of  his 
own.  In  the  case  of  %  Cygni,  he  considers  that  two  perturb- 
ations in  the  period — the  one  of  100,  the  other  of  8^  —  are 
more  probable  than  a  single  period  of  108.  Whether  such 
disturbances  arise  from  changes  in  the  process  of  light  which 
is  going  on  in  the  atmosphere  of  the  star  itself,  or  from  the 
periodic  times  of  some  planet  which  revolves  round  the  fixed 
star  or  sun  %  Cygni,  and  by  attraction  influences  the  form  of 
its  photosphere,  is  still  a  doubtful  question.  The  greatest 
irregularity  in  change  of  intensity  has  unquestionably  been 
exhibited  by  the  variabilis  Scuti  (Sobieski's  shield)  ;  for  this 
star  diminishes  from  the  5-4th  down  to  the  ninth  magnitude  ; 
and,  moreover,  according  to  Pigott,  it  once  totally  disappeared 
at  the  end  of  the  last  century.  At  other  times  the  fluctua- 
tions in  its  brightness  have  been  only  from  the  6-5th  to  the 
sixth  magnitude.  The  maximum  of  the  variations  of%  Cygni 
have  been  between  the  6'7th  and  fourth  magnitude  ;  of  Mira, 
from  the  fourth  to  the  2- 1st  magnitude.  On  the  other  hand, 
in  the  duration  of  its  periods  6  Cephei  shows  an  extraordi- 
nary, and,  indeed,  of  all  variable  stars,  the  greatest  regularity, 
as  is  proved  by  the  87  minima  observed  between  the  10th 
of  October,  1840,  and  8th  of  January,  1848,  and  even  later. 
In  the  case  of  e  Aurigse,  the  variation  of  its  brilliancy,  dis- 
covered by  that  indefatigable  observer,  Heis,  of  Aix-la-Cha 
pelle,*  extends  only  from  the  3'4th  to  the  4'5th  magnitude. 

A  great  difference  in  the  maximum  of  brightness  is  exhib- 
ited by  Mira  Ceti.  In  the  year  1779,  for  instance  (on  the 
6th  of  November),  Mira  was  only  a  little  dimmer  than  Alde- 
baran,  and,  indeed,  not  unfrequently  brighter  than  stars  of 
the  second  magnitude  ;  whereas  at  other  times  this  variable 
star  scarcely  attained  to  the  intensity  of  the  light  of  6  Ceti, 
which  is  of  the  fourth  magnitude.  Its  mean  brightness  is 
equal  to  that  of  y  Ceti  (third  magnitude).  If  we  designate 
by  0  the  brightness  of  the  faintest  star  visible  to  the  naked 
eye,  and  that  of  Aldebaran  by  50,  then  Mira  has  varied  in 
its  maximum  from  20  to  47.  Its  probable  brightness  may  be 
expressed  by  30  :  it  is  oftener  below  than  above  this  limit. 
The  measure  of  its  excess,  however,  when  it  does  occur,  ia 

*  Argelander,  in  Schumacher's  Aslron.  Nachr.,  bd.  xxvi.  (1848),  No, 
624,  s.  369. 


168  COSMOS. 

in  proportion  more  considerable.  No  certain  period  of  these 
oscillations  has  as  yet  been  discovered.  There  are,  however, 
indications  of  a  period  of  40  years,  and  another  of  160. 

The  periods  of  va nation  in  different  stars  vary  as  1:250. 
The  shortest  period  is  unquestionably  that  exhibited  by  (3 
Persei,  being  68  hours  and  49  minutes ;  so  long,  at  least,  as 
that  of  the  polar  star  is  not  established  at  less  than  two  days. 
Next  to  ft  Persei  come  6  Cephei  (5d.  8h.  49m.),  77  Aquilaa 
(7d.  4h.  14m.),  and  $  Geminorum  (lOd.  3h.  35m.).  The 
longest  periods  are  those  of  30  Hydrae  Hevelii,  495  days ; 
X  Cygni,  406  days ;  Variabilis  Aquarii,  388  days  ;  Serpentis 
S.,  367  days ;  and  Mira  Ceti,  332  days.  In  several  of  the 
variable  stars  it  is  well  established  that  they  increase  in  brill- 
iancy more  rapidly  than  they  diminish.  This  phenomenon 
is  the  most  remarkable  in  6  Cephei.  Others,  as,  for  instance, 
ft  Lyrse,  have  an  equal  period  of  augmentation  and  diminu- 
tion of  light.  Occasionally,  indeed,  a  difference  is  observed 
in  this  respect  in  the  same  stars,  though  at  different  epochs 
in  their  process  of  light.  Generally  Mira  Ceti  (as  also  6  Ce- 
phei) is  more  rapid  in  its  augmentation  than  in  its  diminu 
tion  ;  but  in  the  former  the  contrary  has  also  been  observed 

Periods  within  periods  have  been  distinctly  observed  in 
the  case  of  Algol,  of  Mira  Ceti,  of  ft  Lyrao,  and  with  great 
probability  also  in  %  Cygni.  The  decrease  of  the  period  of 
Algol  is  now  unquestioned.  Goodricke  was  unable  to  per- 
ceive it,  but  Argelander  has  since  done  so  ;  in  the  year  1842 
he  was  enabled  to  compare  more  than  100  trustworthy  ob- 
servations (comprising  7600  periods),  of  which  the  extremes 
differed  from  each  other  more  than  58  years.  (Schumacher's 
Astron.  Nachr.,  Nos.  472  and  624.)  The  decrease  in  the 
period  is  becoming  more  and  more  observable.*  For  the 

*  "  If,"  says  Argelander,  "  I  take  for  the  0  epoch  the  minimum  bright- 
ness of  Algol,  in  1800,  on  the  1st  of  January,  at  18h.  1m.  mean  Paris 
time,  I  obtain  the  duration  of  the  periods  for 

—1987,  2d.  20h.  48m.,  or  59s.-416iOs.-316 
—1406,  "  58s.-737iOs.-094 

58s.-393JtOs.-175 
58s.-154-tOs.-039 
58s.-193-tOs.-096 
57s.-971iOs.-045 
558.-182-j-Os.-348 
"  In  this  table  the  numbers  have  the  following  signification :  if  we 
designate  the  minimum  epoch  of  the  1st  of  Jan.,  1800,  by  0,  that  im- 
mediately preceding  by  — 1,  and  that  immediately  following  by  -^-1,  and 
BO  on,  then  the  duration  between  — 1987  and  — 1986  would  be  exactly 
2d.  20h.  48m.  59s  -416.  but  *Jie  duration  between  -f-5441  and  +5442 


VARIABLE    STARS.  169 

periods  of  the  maximum  of  Mira  (including  the  maximum  of 
brightness  observed  by  Fabricius  in  1596),  a  formula*  has 
been  established  by  Argelander,  from  which  all  the  maxima 
can  be  so  deduced  that  the  probable  error  in  a  long  period  of 
variability,  extending  to  33 Id.  8h.,  does  not  in  the  mean  ex- 
ceed 7  days,  while,  on  the  hypothesis  of  a  uniform  period,  it 
would  be  15  days. 

The  double  maximum  and  minimum  of  (3  Lyrae,  in  each 
of  its  periods  of  nearly  13  days,  was  from  the  first  correctly 
ascertained  by  its  discoverer,  Goodricke  (1784)  ;  but  it  has 
been  placed  still  more  beyond  doubtf  by  very  recent  observ- 
ations. It  is  remarkable  that  this  star  attains  to  the  same 
brightness  in  both  its  maxima,  but  in  its  principal  minimum 
it  is  about  half  a  magnitude  fainter  than  in  the  other.  Since 
the  discovery  of  the  variability  of  (3  Lyrae,  the  period  in  a 
period  has  probably  been  on  the  increase.  At  first  the  vari- 
ability was  more  rapid,  then  it  became  gradually  slower ;  and 
this  decrease  in  the  length  of  time  reached  its  limit  between 
the  years  1840  and  1844.  During  that  time  its  period  was 
nearly  invariable  ;  at  present  it  is  again  decidedly  on  the  de- 
crease. Something  similar  to  the  double  maximum  of  (3  Lyrse 
occurs  in  6  Cephei.  There  is  a  tendency  to  a  second  maxi- 

would  be  2d.  20h.  48m.  55s. -182 ;  the  former  applies  to  the  year  1784, 
the  latter  to  the  year  1842. 

"The  numbers  which  follow  the  signs  ^  are  the  probable  errors. 
That  the  diminution  becomes  more  and  more  rapid  is  shown  as  well  by 
the  last  number  as  by  all  my  observations  since  1847." 

*  Argelander's  formula  for  representing  all  observations  of  the  maxima 
of  Mira  Ceti  is,  as  communicated  by  himself,  as  follows : 

1751,  Sep.,  9-76  -f331d.-3363  E. 

+10d.-5,  sin.  (3T6T°°  E.  +86°  23')  +18d.-2,  sin.  (ff°  E.  +231°  42') 
+33d.-9,  sin.  (ff°  E.  +170°  19')  -f  65d.-3,  sin.  (fp  E.  -j-6°  37') 
where  E.  represents  the  number  of  maxima  which  have  occurred  since 
Sept.  9,  1751,  and  the  co-efficients  are  given  in  days.     Therefore,  for 
the  current  year  (E.  being  =109),  the  following  is  the  maximum: 
1751,  Sep.,  9-76+36115d.-G5-|-8d.-44— 12d.-24. 

4-18d.-59+27d.-34=1850,  Sep.,  8d.-54. 

"  The  strongest  evidence  in  favor  of  this  formula  is,  that  it  represents 
even  the  maximum  of  1596  {Cosmos,  vol.  ii.,  p.  330),  which,  on  the 
supposition  of  a  uniform  period,  would  deviate  more  than  100  days. 
However,  the  laws  of  the  variation  of  the  light  of  this  star  appear  so 
complicated,  that  in  particular  cases — e.  g.,  for  the  accurately  observed 
maximum  of  1840 — the  formula  was  wrong  by  many  days  (nearly  twen- 
ty-five)." 

t  Compare  Argelander's  essay,  written  on  the  occasion  of  the  cen- 
tenary jubilee  of  the  KOnigsberg  University,  and  entitled  De  Stella 
8  Lyra;  Variabili,  1844. 

VOL.  III.— H 


170  COSMOS. 

uaum,  in  so  far  as  its  diminution  of  light  does  not  \  •£&/ 
uniformly ;  but,  after  having  been  for  some  time  tolerably 
rapid,  it  comes  to  a  stand,  or  at  least  exhibits  a  very  Incon- 
siderable diminution,  which  suddenly  becomes  rapicj  again. 
In  some  stars  it  would  almost  appear  as  though  th,j  light 
were  prevented  from  fully  attaining  a  second  maximum.  In 
%  Cygni  it  is  very  probable  that  two  periods  of  variability 
prevail — a  longer  one  of  100  years,  and  a  shorter  on;  of  8£. 
The  question  whether,  on  the  whole,  there  is  greater  reg- 
ularity in  variable  stars  of  very  short  than  in  those  of  very 
long  periods,  is  difficult  to  answer.  The  variations  from  a 
uniform  period  can  only  be  taken  relatively ;  i.  e.,  in  parts 
of  the  period  itself.  To  commence  with  long  periods,  ^  Cygni, 
Mira  Ceti,  and  30  Hydrse  must  first  of  all  be  consideied.  In 
X  Cygni,  on  the  supposition  of  a  uniform  variability,  the  devi- 
ations from  a  period  of  406-0634  days  (which  is  the  most 
probable  period)  amount  to  39-4  days.  Even  though  a  por- 
tion of  these  deviations  may  be  owing  to  errors  of  observa- 
tion, still  at  least  29  or  30  days  remain  beyond  doubt ;  i.  e., 
one  fourteenth  of  the  whole  period.  In  the  case  of  Mira 
Ceti,*  in  a  period  of  331 '340  days,  the  deviations  amount  to 
55'5  days,  even  if  we  do  not  reckon  the  observations  of  David 
Fabricius.  If,  allowing  for  errors  of  observation,  we  limit 
the  estimate  to  40  days,  we  still  obtain  one  eighth ;  conse- 
quently, as  compared  with  %  Cygni,  nearly  twice  as  great  a 
deviation.  In  the  case  of  30  Hydrse,  which  has  a  period  of 
495  days,  it  is  still  greater,  probably  one  fifth.  It  is  only 
during  the  last  few  years  (since  1840,  and  still  later)  that  the 
variable  stars  with  very  short  periods  have  been  observed 
steadily  and  with  sufficient  accuracy,  so  that  the  problem  in 
question,  when  applied  to  them,  is  still  more  difficult  of  solu- 
tion. From  the  observations,  however,  which  have  as  yet 
been  taken,  less  considerable  deviations  seem  to  occur.  In 
the  case  of  77  Aquilse  (with  a  period  of  7d.  4h.)  they  only 
amount  to  one  sixteenth  or  one  seventeenth  of  the  whole  pe- 
riod ;  in  that  of  ft  Lyrse  (period  12d.  21h.)  to  one  twenty- 
seventh  or  one  thirtieth ;  but  the  inquiry  is  still  exposed  to 
much  uncertainty  as  regards  the  comparison  of  long  and  short 
periods.  Of  j3  Lyra  between  1700  and  1800  periods  have 
been  observed ;  of  Mira  Ceti,  279  ;  of  %  Cygni,  only  145. 
The  question  that  has  been  mooted,  whether  stars  which 

*  The  work  of  Jacques  Cassini  (Eltmens  £  Astronomic,  1740,  p.  66- 
69)  belongs  to  the  earliest  systematic  attempts  to  investigate  tb?  mean 
duration  of  the  period  of  the  variation  of  Mira  Ceti. 


VARIABLE    STARS.  171 

have  long  appeared  to  be  variable  in  regular  periods  ever 
cease  to  be  so,  must  apparently  be  answered  in  the  nega- 
tive. As  among  the  constantly  variable  stars  there  are 
some  which  at  one  time  exhibit  a  very  great,  and  at  anoth- 
er a  very  small  degree  of  variability  (as,  for  instance,  vari- 
abilis  Scuti),  so,  it  seems,  there  are  also  others  whose  vari- 
ability is  at  certain  times  so  very  slight,  that,  with  our  lim- 
ited means,  we  are  unable  to  detect  it.  To  such  belongs 
variabilis  Coronae  bor.  (No.  5236  in  the  Catalogue  of  the 
British  Association),  recognized  as  variable  by  Pigott,  who 
observed  it  for  a  considerable  time.  In  the  winter  of  1795-6 
this  star  became  totally  invisible  ;  subsequently  it  again 
appeared,  and  the  variations  of  its  light  were  observed  by 
Koch.  In  1 8 1 7 ,  Harding  and  Westphal  found  that  its  bright- 
ness was  nearly  constant,  while  in  1824  Olbers  was  again 
enabled  to  perceive  a  variation  in  its  luminosity.  Its  con- 
stancy now  again  returned,  and  from  August,  1843,  to  Sep- 
tember, 1845,  was  established  by  Argelander.  At  the  end 
of  September,  a  fresh  diminution  of  its  light  commenced. 
By  October,  the  star  was  no  longer  visible  in  the  comet-seek- 
er ;  but  it  appeared  again  in  February,  1846,  and  by  the  be- 
ginning of  June  had  reached  its  usual  magnitude  (the  sixth). 
Since  then  it  has  maintained  this  magnitude,  if  we  overlook 
some  small  fluctuations  whose  very  existence  has  not  been 
established  with  certainty.  To  this  enigmatical  class  of  stars 
belong  also  variabilis  Aquarii,  and  probably  Janson  and  Kep- 
ler's star  in  Cygnus  of  1600,  which  we  have  already  men- 
tioned among  the  new  stars. 


172 


TABLE  OP  THE  VARIABLE  STARS,  BY  F.  ARGELANDEE. 


No.!       Name  of  tli*  Star. 

Length  of 
Period. 

Brigbtnes 

s  in  the 
Minimum. 

NameofniscoTeraraod 
Date  of  DiKjorery. 

1  o  Ceti 

J).     H.   M. 

331  20 

Magnit. 
4to2-l 
23 
6-7  to     4 
5  to     4 
5 
34 
3-4 
43 
3 
6 
6  5  to  5-4 
7to6'7 
9  to  6  7 
67 
8  to  7-8 
7 
2 
1 
2 
34 
4-3 
2 
8 
7-8 

Magnit. 
0 
4 
0 
0 
0 
5-4 
45 
5-4 
34 
0 
9  to     6 
0 
0 
0 
0 
0 
3-2 
1-2 
23 
4-5 
5-4 
2*3 

Holwarda,         1639. 
Montanari,         1669. 
Gottfr.  Kirch,    1687. 
Maraldi,             1704. 
Koch,                 1782. 
E.  Pigott,           1784. 
Goodricke,        1784. 
Ditto,                 1784. 
Wm.  Herschel  1795. 
E.  Pigott,           1795. 
Ditto,                 1795. 
Harding,            1809. 
Ditto,                  1810. 
Ditto,                  1826. 
Ditto,                  1828. 
Schwerd,           1829. 
Birt,                    1831. 
John  Herschel,  1836. 
Ditto,                 1837. 
Heis,                  1846. 
Schmidt,            1847. 
Ditto,                 1848. 
Hind,                 1848. 
Ditto,                 1848. 

210  Perse  i 

22049 
406    1  30 
495  
31218  — 
7-414 
122145 
5    849 
66    8  — 
323  
71  17  — 
145  21  — 
388  13  — 
359  
367    5  — 
380  
79    3  — 
196  
55  
i 

10    335 
4023  — 
350  

i 

3  \x  Cygni 

430  Hydra  He  v.  . 
5LeonisR.,420M. 

6  17  A(|  u  il;i- 

7/3  Lyra 

8  6  Cephei      . 

9  a  Herculis  
10  Coronje  R. 

11  Scuti  R. 

12  Virginia  R  
13Aquarii  R  

14Serpentis  R  
ISSerpentis  S  
l6Cancri  R  

17  a  Cassiopeiae  ... 
18  a  Orionis 

19  o  Hydra  

20eAurigae  

21  f  Geminorum  ... 
22  {3  Pegasi 

23PegasiR  
24CancriS  

EXPLANATORY  REMARKS. 

The  0  in  the  column  of  the  minima  indicates  that  the  star  is  then 
fainter  than  the  tenth  magnitude.  For  the  purpose  of  clearly  and  con- 
veniently designating  the  smaller  variable  stars,  which  for  the  most  part 
have  neither  names  nor  other  designations,  I  have  allowed  myself  to  ap- 

C,d  to  them  capitals,  since  the  letters  of  the  Greek  and  the  smaller 
in  alphabet  have,  for  the  most  part,  been  already  employed  by 
Bayer. 

Besides  the  stars  adduced  in  the  preceding  table,  there  are  almost  as 
many  more  which  are  supposed  to  be  variable,  since  their  magnitudes 
are  set  down  differently  by  different  observers.  But  as  these  estimates 
were  merely  occasional,  and  have  not  been  conducted  with  much  pre- 
cision, and  as  different  astronomers  have  different  principles  in  estima- 
ting magnitudes,  it  seems  the  safer  course  not  to  notice  any  euch  cases 
until  the  same  observer  shall  have  found  a  decided  variation  in  them  at 
different  times.  With  all  those  adduced  in  the  table,  this  is  the  case ; 
and  the  fact  of  their  periodical  change  of  light  is  quite  established,  even 
where  the  period  itself  has  not  been  ascertained.  The  periods  given  in 
the  table  are  founded,  for  the  most  part,  on  my  own  examination  of  all 
the  earlier  observations  that  have  been  published,  and  on  my  own  ob- 
servations within  the  last  ten  years,  which  have  not  as  yet  been  pub- 
lished. Exceptions  will  be  mentioned  in  the  following  notices  of  the 
several  stars. 

In  these  notices  the  positions  are  those  for  1850,  and  are  expressed  in 


VARIABLE    STARS.  173 

right  ascension  and  declination.  The  frequently-repeated  term  grada- 
tion indicates  a  difference  of  brightness,  which  may  be  distinctly  recog- 
nized even  by  the  naked  eye,  or,  in  the  case  of  those  stars  which  are 
invisible  to  the  unaided  sight,  by  a  Frauenhofer's  comet-seeker  of  twen- 
ty-five and  a  half  inches  focal  length.  For  the  brighter  stars  above  the 
sixth  magnitude,  a  gradation  indicates  about  the  tenth  part  of  the  dif- 
ference by  which  the  successive  orders  of  magnitude  differ  from  one  an- 
other ;  for  the  smaller  stars  the  usual  classifications  of  magnitude  are 
considerably  closer. 

(l)o  Ceti,  R.  A.  32°  57',  Decl.  —3°  40' ;  also  called  Mira,  on  account 
of  the  wonderful  change  of  light  which  was  first  observed  in  this  star. 
As  early  as  the  latter  half  of  the  seventeenth  century,  the  periodicity  of 
this  star  was  recognized,  and  Bouillaud  fixed  the  duration  of  its  period 
at  333  days ;  it  was  found,  however,  at  the  same  time,  that  this  dura- 
tion was  sometimes  longer  and  sometimes  shorter,  and  that  the  star,  at 
its  greatest  brilliancy,  appeared  sometimes  brighter  and  sometimes  faint- 
er. This  has  been  subsequently  fully  confirmed.  Whether  the  star  ever 
becomes  perfectly  invisible  is  as  yet  undecided;  at  one  time,  at  the 
epoch  of  its  minimum,  it  has  been  observed  of  the  eleventh  or  twelfth 
magnitude ;  at  another,  it  could  not  be  seen  even  with  the  aid  of  a  three 
or  a  four-feet  telescope.  This  much  is  certain,  that  for  a  long  period  it 
is  fainter  than  stars  of  the  tenth  magnitude.  But  few  observations  of 
the  star  at  this  stage  have  as  yet  been  taken,  most  having  commenced 
when  it  had  begun  to  be  visible  to  the  naked  eye  as  a  star  of  the  sixth 
magnitude.  From  this  period  the  star  increases  in  brightness  at  first 
with  great  rapidity,  afterward  more  slowly,  and  at  last  with  a  scarcely 
perceptible  augmentation ;  then,  again,  it  diminishes  at  first  slowly,  aft- 
erward rapidly.  On  a  mean,  the  period  of  augmentation  of  light  from 
the  sixth  magnitude  extends  to  fifty  days ;  that  of  its  decrease  down  to 
the  same  degree  of  brightness  takes  sixty-nine  days ;  so  that  the  star  is 
visible  to  the  naked  eye  for  about  four  months.  However,  this  is  only 
the  mean  duration  of  its  visibility ;  occasionally  it  has  lasted  as  long  as 
five  months,  whereas  at  other  times  it  has  not  been  visible  for  more  than 
three.  In  the  same  way,  also,  the  duration  both  of  the  augmentation 
and  of  the  diminution  of  its  light  is  subject  to  great  fluctuations,  and  the 
former  is  at  all  times  slower  than  the  latter ;  as,  for  instance,  in  the  year 
1840,  when  the  star  took  sixty-two  days  to  arrive  at  its  greatest  bright- 
ness, and  then  in  forty-nine  days  became  visible  to  the  naked  eye.  The 
shortest  period  of  increase  that  has  as  yet  been  observed  took  place  in 
1679,  and  lasted  only  thirty  days;  the  longest  (of  sixty-seven  days)  oc- 
curred in  1709.  The  decrease  of  light  lasted  the  longest  in  1839,  being 
then  ninety-one  days ;  the  shortest  in  the  year  1660,  when  it  was  com- 
pleted in  nearly  fifty-two  days.  Occasionally,  the  star,  at  the  period  of 
its  greatest  brightness,  exhibits  for  a  whole  month  together  scarcely  any 
perceptible  variation;  at  others,  a  difference  may  be  observed  within  a 
very  fe  w  days.  On  some  occasions,  after  the  star  had  decreased  in  bright- 
ness for  several  weeks,  there  was  a  period  of  perfect  cessation,  or,  at 
least,  a  scarcely  perceptible  diminution  of  light  during  several  days ;  this 
was  the  case  in  1678  and  in  1847. 

The  maximum  brightness,  as  already  remarked,  is  by  no  means  al- 
ways the  same.  If  we  indicate  the  brightness  of  the  faintest  star  that 
is  visible  to  the  naked  eye  by  0,  and  that  of  Aldebaran  (a  Tauri),  a  star 
of  the  first  magnitude,  by  fifty,  then  the  maximum  of  light  of  Mira  fluc- 
tuates between  20  and  47,  i.  e.,  between  the  brightness  of  a  star  of  the 
fourth,  and  of  the  first  or  second  magnitude :  the  mean  brightness  is  28 


174  COSMOS. 

or  that  of  the  star  y  Ceti.  But  the  duration  of  its  periods  is  still  more 
irregular:  its  mean  is  33 Id.  20h.,  while  its  fluctuations  have  extended 
to  a  month ;  for  the  shortest  time  that  ever  elapsed  from  one  maximum 
to  the  next  was  only  306  days,  the  longest,  on  the  other  hand,  367  days. 
These  irregularities  become  the  more  remarkable  when  we  compare  the 
several  occurrences  of  greatest  brightness  with  those  which  would  take 
place  if  we  were  to  calculate  these  maxima  on  the  hypothesis  of  a  uni- 
form period.  The  difference  between  calculation  and  observation  then 
amounts  to  50  days,  and  it  appears  that,  for  several  years  in  succession, 
those  differences  are  nearly  the  same,  and  in  the  same  direction.  This 
evidently  indicates  that  the  disturbance  in  the  phenomena  of  light  is  one 
of  a  very  long  period.  More  accurate  calculations,  however,  have  prov- 
ed that  the  supposition  of  one  disturbance  is  not  sufficient,  and  that  sev- 
eral must  be  assumed,  which  may,  however,  all  arise  from  the  same 
cause ;  one  of  these  recurs  after  1 1  single  periods ;  a  second  after  88 ; 
a  third  after  176 ;  and  a  fourth  after  264.  From  hence  arises  the  form- 
ula of  sines  (given  at  p.  169,  note  *),  with  which,  indeed,  the  several 
maxima  very  nearly  accord,  although  deviations  still  exist  which  can 
not  be  explained  by  errors  of  observation. 

(2)  (3  Persei,  Algol ;  R.  A.  44°  36',  Decl.  4-40°  22'.    Although  Gemi- 
niano  Montanari  observed  the  variability  or  this  star  in  1667,  and  Ma- 
raldi  likewise  noticed  it,  it  was  Goodricke  that  first,  in  1782,  discovered 
the  regularity  of  the  variability.     The  cause  of  this  is  probably  that  this 
star  does  not,  like  most  other  variable  ones,  gradually  increase  and  di- 
minish in  brightness,  but  for  2d.  13h.  shines  uniformly  as  a  star  of  the 
2-3d  magnitude,  and  only  appears  less  bright  for  seven  or  eight  hours, 
when  it  sinks  to  the  fourth  magnitude.     The  augmentation  and  dimi- 
nution of  its  brightness  are  not  quite  regular;  but  when  near  to  the 
minimum,  they  proceed  with  greater  rapidity;  whence  the  time  of 
least  brightness  may  be  accurately  calculated  to  within  ten  to  fifteen 
minutes.    It  is  moreover  remarkable  that  this  star,  after  having  increased 
in  light  for  about  an  hour,  remains  for  nearly  the  same  period  at  the 
same  brightness,  and  then  begins  once  more  perceptibly  to  increase 
Till  very  recently  the  duration  of  the  period  was  held  to  be  perfectly- 
uniform,  and  Wurm  was  able  to  present  all  observations  pretty  closely 
by  assuming  it  to  be  2d.  21h.  48m.  58is.    However,  a  more  ai  curate  cal- 
culation, in  which  was  comprehended  a  space  of  time  nearly-  twice  as 
long  as  that  at  Wurm's  command,  has  shown  that  the  period  becomes 
gradually  shorter.     In  the  year  1784  it  was  2d.  20h.  48m.  59-4s.,  and  in 
the  year  1842  only  2d.  20h.  48m.  55-2s.     Moreover,  from  the  most  re- 
cent observations,  it  becomes  very  probable  that  this  diminution  of  the 
period  is  at  present  proceeding  more  rapidly  than  before,  so  that  for  this 
star  also  a  formula  of  sines  for  the  disturbance  of  its  period  will  in  time 
be  obtained.     Besides,  this  diminution  will  be  accounted  for  if  we  as- 
sume that  Algol  comes  nearer  to  us  by  about  2000  miles  every  year,  or 
recedes  from  us  thus  far  less  each  succeeding  year ;  for  in  that  case  his 
light  would  reach  us  as  much  sooner  every  year  as  the  decrease  of  the 
period  requires;  *.  e.,  about  the  twelve  thousandth  of  a  second.     If  this 
be  the  true  cause,  a  formula  of  sines  must  eventually  be  deduced. 

(3)  X  Cygni,  R.  A.  296°  12',  Decl.  +32°  32'.     This  star  also  exhibits 
nearly  the  same  irregularities  as  Mira.     The  deviations  of  the  observed 
maxima  from  those  calculated  for  a  uniform  period  amount  to  forty  days, 
but  are  considerably  diminished  by  the  introduction  of  a  disturbance 
of  8J^  single  periods,  and  of  another  of  100  such  periods.     In  its  maxi- 
mum this  star  reaches  the  mean  brightness  of  a  faint  fifth  magnitude,  or 


VARIABLE    STARS.  175 

one  gradat/on  brighter  than  the  star  17  Cygni.  The  fluctuations,  how 
ever,  are  in  this  case  also  very  considerable,  and  have  been  observed 
from  thirteen  gradations  below  the  mean  to  ten  above  it.  At  this  low- 
est maximum  the  star  would  be  perfectly  invisible  to  the  naked  eye, 
whereas,  on  the  contrary,  in  the  year  1847,  it  could  be  seen  without 
the  aid  of  a  telescope  for  fully  ninety-seven  days ;  its  mean  visibility 
extends  to  fifty-two  days,  of  which,  on  the  mean,  it  is  twenty  days  on 
the  increase,  and  thirty-two  on  the  decrease. 

(4)  30  Hydras  Hevetii,  E.  A.  200°  23',  Decl.  —22°  30'.     Of  this  star, 
which,  from  its  position  in  the  heavens,  is  only  visible  for  a  short  time 
during  every  year,  all  that  can  be  said  is,  that  both  its  period  and  its 
maximum  brightness  are  subject  to  very  great  irregularities. 

(5)  Leonis  R.  =420  Mayeri;  R.  A.  144°  52',  Decl.  -f  12°  7'.     This 
star  is  often  confounded  with  18  and  19  Leonis,  which  are  close  to  it, 
and,  in  consequence,  has  been  very  little  observed ;  sufficiently,  how- 
ever, to  show  that  the  period  is  somewhat  irregular.     Its  brightness  at 
the  maximum  seems  also  to  fluctuate  through  some  gradations. 

(6)  n  Aquilss,  called  also  y  Antinoi ;  R.  A.  296°  12',  Decl.  +0°  37'. 
The  period  of  this  star  is  tolerably  uniform,  7d.  4h.  13m.  53s. ;  observa- 
tions, however,  prove  that  at  long  intervals  of  time  trifling  fluctuations 
occur  in  it,  not  amounting  to  more  than  20  seconds.     The  variation  of 
light  proceeds  so  regularly,  that  up  to  the  present  time  no  deviations 
have  been  discovered  which  could  not  be  accounted  for  by  errors  of  ob- 
servation.    In  its  minimum,  this  star  is  one  gradation  fainter  than  i 
Aquilis ;  at  first  it  increases  slowly,  then  more  rapidly,  and  afterward 
again  more  slowly ;  and  in  2d.  9h.  from  its  minimum,  attains  to  its  great- 
est brightness,  in  which  it  is  nearly  three  gradations  brighter  than  /?, 
but  two  fainter  than  6  Aquilse.     From  the  maximum  its  brightness  does 
not  diminish  quite  so  regularly;  for  when  the  star  has  reached  the  bright- 
ness of  (3  (*.  e.,  in  Id.  lOh.  after  the  maximum),  it  changes  more  slowly 
than  either  before  or  afterward. 

(7)  /3  Lyra;,  R.  A.  281°  8',  Decl.  -f-33°  11';  a  star  remarkable  from 
the  fact  of  its  having  two  maxima  and  two  minima.     When  it  has  been 
at  its  faintest  light,  one  third  of  a  gradation  fainter  than  f  Lyrse,  it  rises 
in  3d.  5h.  to  its  first  maximum,  in  which  it  remains  three  fourths  of  a 
gradation  fainter  than  y  Lyrse.     It  then  sinks  in  3d.  3h.  to  its  second 
minimum,  in  which  its  light  is  about  five  gradations  greater  than  that  of 
f.     After  3d.  2h.  more,  it  again  reaches,  in  its  second  maximum,  to  the 
brightness  of  the  first ;  and  afterward,  in  3d.  12h.,  declines  once  more 
to  its  greatest  faintness;  so  that  in  12d.  21h.  46m.  40s.  it  runs  through 
all  its  variations  of  light.     This  duration  of  the  period,  however,  only 
applies  to  the  years  1840  to  1844;    previously  it  had  been  shorter — in 
the  year  1784,  by  about  2^h ;  in  1817  and  1818,  by  more  than  an  hour ; 
and  at  present,  a  shortening  of  it  is  again  clearly  perceptible.     There 
is,  therefore,  no  doubt  that  in  the  case  of  this  star  the  disturbance  of  its 
period  may  be  expressed  by  a  formula  of  sines. 

(8)  6  Cephei,  R.  A.  335°  54',  Decl.  +57°  39'.     Of  all  the  known  va- 
riable stars,  this  exhibits  in  every  respect  the  greatest  regularity.     The 
period  of  5d.  8h.  47m.  39is.  is  given  by  all  the  observations  from  1784 
to  the  present  day,  allowing  for  errors  of  observation,  which  will  ac- 
count for  all  the  slight  differences  exhibited  in  the  course  of  the  altern 
ations  of  light.     This  star  is  in  its  minimum  three  quarters  of  a  gradation 
brighter  than  e ;  in  its  maximum  it  resembles  i  of  the  same  constellation 
(Cepheus).     It  takes  Id.  15h.  to  pass  from  the  former  to  the  latter ;  but, 
on  the  other  hand,  more  than  double  that  time,  viz.,  3d.  18h.,  to  change 


176  COSMOS. 

again  to  its  minimum    during  eight  hours  of  the  latter  period,  however 
it  scarcely  changes  at  all,  and  very  inconsiderably  for  a  whole  day. 

(9)  a  Herculis,  R.  A.  256°  57',  Decl.  +14°  34';  an  extremely  red 
double  star,  the  variation  of  whose  light  is  in  every  respect  very  irreg- 
ular.    Frequently,  its  light  scarcely  changes  for  months  together;  at 
other  times,  in  the  maximum,  it  is  nearly  five  gradations  brighter  than 
in  the  minimum ;  consequently,  the  period  also  is  still  very  uncertain. 
The  discoverer  of  the  star's  variation  had  assumed  it  to  be  sixty-three 
days.     I  at  first  set  it  down  at  ninety-five,  until  a  careful  reduction  of  all 
iny  observations,  made  during  seven  years,  at  length  gave  me  the  peri- 
od assigned  in  the  text.     Heis  believes  that  he  can  represent  all  the  ob- 
servations by  assuming  a  period  of  184-9  days,  with  two  maxima  and 

(10)  Corona;  R.,  R.  A.  235°  36',  Decl.  +28°  37'.     This  star  is  varia- 
ble only  at  times ;  the  period  set  down  has  been  calculated  by  Koch 
from  his  own  observations,  which  unfortunately  have  been  lost. 

(11)  Scuti  R.,  R.  A.  279°  52',  Decl.  —5°  51'.     The  variations  of  bright- 
ness of  this  star  are  at  times  confined  within  a  very  few  gradations, 
whereas  at  others  it  diminishes  from  the  fifth  to  the  ninth  magnitude.     It 
has  been  too  little  observed  to  determine  when  any  fixed  rule  prevails 
in  these  deviations.     The  duration  of  the  period  is  also  subject  to  con- 
siderable fluctuations. 

(12)  Virginis  R.,  R.  A.  187°  43',  Decl.  +7°  49'.     It  maintains  its  pe- 
riod and  its  maximum  brightness  •with  tolerable  regularity ;  some  devi- 
ations, however,  do  occur,  which  appear  to  me  too  considerable  to  be 
ascribed  merely  to  errors  of  observation. 

(13)  Aquarii  R.,  R.  A.  354°  11',  Decl.  —16°  6'. 

(14)  Serpentis  R.,  R.  A.  235°  57',  Decl.  -f  15°  3.T. 

(15)  Serpentis  S.,  R.  A.  228°  40',  Decl.  -f  14°  o^'. 

(16)  Cancri  R.,  R.  A.  122°  6',  Decl.  4-12°  9'. 

Of  these  four  stars,  which  have  been  but  very  slightly  observed,  little 
more  can  be  said  than  what  is  given  in  the  table. 

(17)  a  Cassiopeia,  R.  A.  8°  0',  Decl.  +55°  43'.    This  star  is  very  diffi- 
cult to  observe.     The  difference  between  its  maximum  and  minimum 
only  amounts  to  a  few  gradations,  and  is,  moreover,  as  variable  as  the 
duration  of  the  period.     This  circumstance  explains  the  varying  state- 
ments on  this  head.     That  which  I  have  given,  which  satisfactorily  rep- 
resents the  observations  from  1782  to  1849,  appears  to  me  the  most  prob- 
able one. 

(18)  a  Orionis,  R.  A.  86°  46',  Decl.  +7°  22'.     The  variation  in  the 
light  of  this  star  likewise  amounts  to  only  four  gradations  from  the  min- 
imum to  the  maximum.     For  91^  days  it  increases  in  brightness,  while 
its  diminution  extends  over  104-fc,  and  is  imperceptible  from  the  twen- 
tieth to  the  seventieth  day  after  the  maximum.     Occasionally  its  varia 
bility  is  scarcely  noticeable.     It  is  a  very  red  star. 

(19)  a  Hydras,  R.  A.  140°  3',  Decl.  —8°  1'.     Of  all  the  variable  stars, 
this  is  the  most  difficult  to  observe,  and  its  period  is  still  altogether  un- 
certain.    Sir  John  Herschel  sets  it  down  at  from  twenty-nine  to  thirty 

§1)  e  Aurigae,  R.  A.  72°  48',  Decl.  -f  43°  36'.     The  alternation  of 
in  this  star  is  either  extremely  irregular,  or  else,  in  a  period  of  sev- 
eral years,  there  are  several  maxima  and  minima — a  question  which  can 
not  be  decided  for  many  years. 

(21)  f  Geminorum,  R.  A.  103°  48',  Decl.  +20°  47'.     This  star  has 
hitherto  exhibited  a  perfectly  regular  course  in  the  variations  of  its  ligbt 


VARIABLE    STARS.  177 

Ita  brightness  at  its  minimum  keeps  the  mean  between  v  and  v  of  the 
same  constellation ;  in  the  maximum  it  does  not  quite  reach  that  of  A. 
It  takes  4d.  21h.  to  attain  its  full  brightness,  and  5d.  6h.  for  its  diminu- 
tion. 

(22)  0  Pegasi,  R.  A.  344°  7',  Decl.  -j-27°  16'.     Its  period  is  pretty 
well  ascertained,  but  as  to  the  course  of  its  variation  of  light  nothing  can 
as  yet  be  asserted. 

(23)  Pegasi  R.,  R.  A.  344°  47'.  Decl.  +9°  43'. 

(24)  Cancri  8.,  R.  A.  128°  50',  Decl.  +19°  34'. 
Of  these  two  stars  nothing  at  present  can  be  said. 

FK.  ARGELANDBR. 

Bonn,  August,  1850. 

VARIATION  OF  LIGHT  IN  STARS  WHOSE  PERIODICITY  is 
UNASCERTAINED. — In  the  scientific  investigation  of  important 
natural  phenomena,  either  in  the  terrestrial  or  in  the  sidereal 
sphere  of  the  Cosmos,  it  is  imprudent  to  connect  together, 
without  due  consideration,  subjects  which,  as  regards  their 
proximate  causes,  are  still  involved  in  obscurity.  On  this 
account  we  are  careful  to  distinguish  stars  which  have  ap- 
pe^red  and  again  totally  disappeared  (as  in  the  star  in  Cas- 
siopeia, 1572) ;  stars  which  have  newly  appeared  and  not 
again  disappeared  (as  that  in  Cygnus,  1600) ;  variable  stars 
with  ascertained  periods  (Mira  Ceti,  Algol)  ;  and  stars  whose 
intensity  of  light  varies,  of  whose  variation,  however,  the  pe- 
riodicity is  as  yet  unascertained  (as  i\  Argus).  It  is  by  no 
means  improbable,  but  still  does  not  necessarily  follow,  that 
these  four  kinds  of  phenomena*  have  perfectly  similar  causes 
in  the  photospheres  of  those  remote  suns,  or  in  the  nature  of 
their  surfaces. 

As  we  commenced  our  account  of  new  stars  with  the  most 
remarkable  of  this  class  of  celestial  phenomena — the  sudden 
appearance  of  Tycho  Brahe's  star — so,  influenced  by  similar 
considerations,  we  shall  begin  our  statements  concerning  the 
variable  stars  whose  periods  have  not  yet  been  ascertained, 
with  the  unperiodical  fluctuations  in  the  light  of  77  Argus, 
which  to  the  present  day  are  still  observable.  This  star  is 
situated  in  the  great  and  magnificent  constellation  of  the 

*  Newton  (Philos.  Nat.  Principia  Mathem.,  ed.  Le  Seur  et  Jacquier, 
1760,  torn,  iii.,  p.  671)  distinguishes  only  two  kinds  of  these  sidereal 
phenomena.  "  Stella?  fixse  quae  per  vices  apparent  et  evanescunt,  quae- 
quo  paulatim  crescunt,  videntur  revolvendo  partem  lucidam  et  partem 
obscuram  per  vices  ostendere."  The  fixed  stars,  which  alternately  ap. 
pear  and  vanish,  and  which  gradually  increase,  appear  by  turns  to  show 
an  illuminated  and  a  dark  side.  This  explanation  of  the  variation  of 
light  had  been  still  earlier  advanced  by  Riccioli.  With  respect  to  the 
caution  necessary  in  predicating  periodicity,  see  the  valuable  remarks 
of  Sir  John  Herschel,  in  his  Observations  at  the  Cape,  $  261. 

K2 


178  COSMOS. 

Ship,  "  the  glory  of  the  southern  skies."  Halley,  as  long 
ago  as  1677,  on  his  return  from  his  voyage  to  St.  Helena, 
expressed  strong  doubts  concerning  the  alternation  of  light 
in  the  stars  of  Argo,  especially  on  the  shield  of  the  prow  and 
on  the  deck  (damdiaKT]  and  KardoTpufid),  whose  relative  or- 
ders of  magnitude  had  been  given  by  Ptolemy.*  However, 
in  consequence  of  the  little  reliance  that  can  be  placed  on 
the  positions  of  the  stars  as  set  down  by  the  ancients,  of  the 
various  readings  in  the  several  MSS.  of  the  Almagest,  and 
of  the  vague  estimates  of  intensity  of  light,  these  doubts  failed 
to  lead  to  any  result.  According  to  Halley's  observation  in 
1677,  r)  Argus  was  of  the  fourth  magnitude  ;  and  by  1751 
it  was  already  of  the  second,  as  observed  by  Lacaille.  The 
star  must  have  afterward  returned  to  its  fainter  light,  for 
Burchell,  during  his  residence  in  Southern  Africa,  from  1811 
to  1815,  found  it  of  the  fourth  magnitude ;  from  1822  to  1826 
it  was  of  the  second,  as  seen  by  Fallows  and  Brisbane ;  in 
February,  1827,  Burchell,  who  happened  at  that  time  to  be 
at  San  Paolo,  in  Brazil,  found  it  of  the  first  magnitude,  per- 
fectly equal  to  a  Crucis.  After  a  year  the  star  returned  to 
the  second  magnitude.  It  was  of  this  magnitude  when  Bur- 
chell saw  it  on  the  29th  of  February,  1828,  in  the  Brazilian 
town  of  Goyaz  ;  and  it  is  thus  set  down  by- Johnson  and  Tay- 
lor, in  their  catalogues  for  the  period  between  1829  and  1833. 
Sir  John  Herschel  also,  at  the  Cape  of  Good  Hope,  estimated 
it  as  being  between  the  second  and  first  magnitude,  from 
1834  to  1837. 

When,  on  the  16th  of  December,  1837,  this  famous  astron- 
omer was  preparing  to  take  the  photometric  measurements 
of  the  innumerable  telescopic  stars,  between  the  eleventh 
and  sixteenth  magnitudes,  which  compose  the  splendid  neb- 
ula around  77  Argus,  he  was  astonished  to  find  this  star,  which 
had  so  often  before  been  observed,  increase  to  such  intensity 
of  light  that  it  almost  equaled  the  brightness  of  a  Centauri, 
and  exceeded  that  of  all  other  stars  of  the  first  magnitude, 
except  Canopus  and  Sirius.  By  the  2d  of  January,  1838,  it 
had  for  that  time  reached  the  maximum  of  its  brightness. 
It  soon  became  fainter  than  Arcturus  ;  but  in  the  middle  of 
April,  1838,  it  still  surpassed  Aldebaran.  Up  to  March, 
1843,  it  continued  to  diminish,  but  was  even  then  a  star  of 
the  first  magnitude  ;  after  that  time,  and  especially  in  April, 
1843,  it  began  to  increase  so  much  in  light,  that,  according 

*  Delambre,  Hist,  de  VAstron.  Ancicnne,  torn,  ii.,  p.  280,  arid  Hist,  de 
I'Attron.  au  IScme  Siecle,  p.  119. 


VARIABLE    STARS.  179 

to  the  observations  of  Mackay  at  Calcutta,  and  Maclear  at 
the  Cape,  77  Argus  became  more  brilliant  than  Canopus,  and 
almost  equal  to  Sirius.*  This  intensity  of  light  was  contin- 
ued almost  up  to  the  beginning  of  the  present  year  (1850). 
A  distinguished  observer,  Lieutenant  Gilliss,  who  commands 
the  astronomical  expedition  sent  by  the  government  of  the 
United  States  to  the  coast  of  Chili,  writes  from  Santiago, 
in  February,  1850  :  "  rj  Argus,  with  its  yellowish-red  light, 
which  is  darker  than  that  of  Mars,  is  at  present  next  in  brill- 
iancy to  Canopus,  and  is  brighter  than  the  united  light  of 
a  Centauri."t  Since  the  appearance  of  the  new  stars  in 
Ophiuchus  in  1604,  no  fixed  star  has  attained  to  such  an  in- 
tensity of  light,  and  for  so  long  a  period — now  nearly  seven 
years.  In  the  173  years  (from  1677  to  1850)  during  which 
we  have  reports  of  the  magnitude  of  this  beautiful  star  in 
Argo,  it  has  undergone  from  eight  to  nine  oscillations  in  the 
augmentation  and  diminution  of  its  light.  As  an  incitement 
to  astronomers  to  continue  their  observations  on  the  phenom- 
enon of  a  great  but  unperiodical  variability  in  rj  Argus,  it  was 
fortunate  that  its  appearance  was  coincident  with  the  famous 
five  years'  expedition  of  Sir  John  Herschel  to  the  Cape. 

In  the  case  of  several  other  stars,  both  isolated  and  double, 
observed  by  Struve  (Stellarum  compos.  Mensurce  Microm., 
p.  Ixxi.-lxxiii.),  similar  variations  of  light  have  been  no- 
ticed, which  have  not  as  yet  been  ascertained  to  be  period- 
ical. The  instances  which  we  shall  content  ourselves  with 
adducing  are  founded  on  actual  photometrical  estimations 
and  calculations  made  by  the  same  astronomer  at  different 
times,  and  not  on  the  alphabetical  series  of  Bayer's  Uranom- 
etry.  In  his  treatise  De  fide  Uranometricz  Bayeriante, 
1842  (p.  15),  Argelander  has  satisfactorily  shown  that  Bayer 
did  not  by  any  means  follow  the  plan  of  designating  the 
brightest  stars  by  the  first  letters  of  the  alphabet ;  but  that, 
on  the  contrary,  he  arranged  the  letters  by  which  he  desig- 
nated stars  of  equal  magnitude  according  to  the  positions  of 

*  Compare  Sir  John  Herschel's  Observations  at  the  Cape,  $  71-78; 
and  Outlines  of  Astron.,  $  830  (Cosmos,  vol.  i.,  p.  153). 

t  Letter  of  Lieutenant  Gilliss,  astronomer  of  the  Observatory  at  Wash- 
ington, to  Dr.  Fid  gel,  consul  of  the  United  States  of  North  America  at 
Leipsic  (in  manuscript).  The  cloudless  purity  and  transparency  of  the 
atmosphere,  which  last  for  eight  months,  at  Santiago,  in  Chili,  are  so 
great,  that  Lieutenant  Gilliss  (with  the  first  great  telescope  ever  con- 
structed in  America,  having  a  diameter  ol  seven  inches,  constructed  by 
Henry  Fitz,  of  New  York,  and  William  Young,  of  Philadelphia)  wa» 
able  clearly  to  recognize  the  sixth  star  in  the  trapezium  of  Orion. 


180  COSMOS. 

the  stars  in  a  constellation,  beginning  usually  at  the  head, 
and  proceeding,  in  regular  order,  down  to  the  feet.  The  or- 
der of  letters  in  Bayer's  Uranometria  has  long  led  to  a  be- 
lief that  a  change  of  light  has  taken  place  in  a  Aquilae,  in 
Castor  Geminorum,  and  in  Alphard  of  Hydra. 

Struve,  in  1838,  and  Sir  John  Hersohel,  observed  Capella 
increase  in  light.  The  latter  now  finds  Capella  much  bright- 
er than  Vega,  though  he  had  always  before  considered  it 
fainter.*  Galle  and  Heis  come  to  the  same  conclusion,  from 
their  present  comparison  of  Capella  and  Vega.  The  latter 
finds  Vega  between  five  and  six  gradations,  consequently 
more  than  half  a  magnitude,  the  fainter  of  the  two. 

The  variations  in  the  light  of  some  stars  in  the  constella- 
tions of  the  Greater  and  of  the  Lesser  Bear  are  deserving  of 
especial  notice.  "  The  star  77  Ursae  majoris,"  says  Sir  John 
Herschel,  "is  at  present  certainly  the  most  brilliant  of  the 
seven  bright  stars  in  the  Great  Bear,  although,  in  1837,  e 
unquestionably  held  the  first  place  among  them."  This  re- 
mark induced  me  to  consult  Heis,  who  so  zealously  and  care- 
fully occupies  himself  with  the  variability  of  stellar  light. 
"  The  following,"  he  writes,  "  is  the  order  of  magnitude  which 
results  from  my  observations,  carried  on  at  Aix-la-Chapelle 
between  1842  and  1850  :  1.  £  Ursse  majoris,  or  Alioth ;  2. 
a,  or  Dubhe  ;  3.  r\,  or  Benetnasch  ;  4.  6,  or  Mizar  ;  5.  /3  ;  6. 
;  7.  6.  The  three  stars,  e,  a,  and  rj,  of  this  group,  are  near- 
y  equal  in  brightness,  so  that  the  slightest  want  of  clearness 
in  the  atmosphere  might  render  their  order  doubtful ;  £  is  de- 
cidedly fainter  than  the  three  before  mentioned.  The  two 
stars  ft  and  y  (both  of  which  are  decidedly  duller  than  £)  are 
nearly  equal  to  each  other ;  lastly,  6,  which  in  ancient  maps  is 
usually  set  down  as  of  the  same  magnitude  with  ft  and  y,  is 
by  more  than  a  magnitude  fainter  than  these  ;  e  is  decided- 
ly variable.  Although  in  general  this  star  is  brighter,  I  have 
nevertheless,  in  three  years,  observed  it  on  five  occasions  to 
be  undoubtedly  fainter  than  a.  I  also  consider  ft  Ursre  ma- 
joris to  be  variable,  though  I  am  unable  to  give  any  fixed 
periods.  In  the  years  1840  and  1841,  Sir  John  Herschel 
found  ft  UrszB  minoris  much  brighter  than  the  Polar  star  ; 
whereas  still  earlier,  in  May,  1846,  the  contrary  was  ob- 

*  Sir  John  Herschel  (  Observations  at  the  Cape,  p.  334,  350,  note  1,  and 
440).  For  older  observations  of  Capella  and  Vega,  see  William  Her- 
schel,  in  the  Philos.  Transact.,  1797,  p.  307,  1799,  p.  121 ;  and  Bode's 
Jahrbuchfur  1810,  B.  148.  Argelander,  on  the  other  hand,  advances 
many  doubts  as  to  the  variation  of  Capella  and  of  the  stars  of  the  Bear. 


r, 


VARIABLE    STARS.  181 

served  by  him.  He  also  conjectures  (3  to  be  variable.*  Since 
1843,  I  have,  as  a  rule,  found  Polaris  fainter  than  ft  Urssa 
minoris  ;  but  from  October,  1843,  to  July,  1849,  Polaris  was, 
according  to  my  registers,  fourteen  times  brighter  than  (3.  I 
have  had  frequent  opportunities  of  convincing  myself  that  the 
color  of  the  last-named  star  is  not  always  equally  red  ;  it  is 
at  times  more  or  less  yellow,  at  others  most  decidedly  red."f 
All  the  pains  and  labor  spent  in  determining  the  relative 
brightness  of  the  stars  will  never  attain  any  certain  result 
until  the  arrangement  of  their  magnitudes  from  mere  esti- 
mation shall  have  given  place  to  methods  of  measurement 
founded  on  the  progress  of  modern  optical  science.J  The 
possibility  of  attaining  such  an  object  need  not  be  despaired 
of  by  astronomers  and  physicists. 

The  probably  great  physical  similarity  in  the  process  of 
light  in  all  self-luminous  stars  (in  the  central  body  of  our  own 
planetary  system,  and  in  the  distant  suns  or  fixed  stars)  has 
long  and  justly  directed  attention  to  the  importance  §  and 
significance  which  attach  to  the  periodical  or  non-periodical 
variation  in  the  light  of  the  stars  in  reference  to  climatology 
generally  ;  to  the  history  of  the  atmosphere,  or  the  varying 
temperature  which  our  planet  has  derived  in  the  course  of 
thousands  of  years  from  the  radiation  of  the  sun ;  with  the 
condition  of  organic  life,  and  its  forms  of  development  in  dif- 
ferent degrees  of  latitude.  The  variable  star  in  the  neck  of 
the  Whale  (Mira  Ceti)  changes  from  the  second  magnitude 
to  the  eleventh,  and  sometimes  vanishes  altogether ;  we  have 
seen  that  t\  Argus  has  increased  from  the  fourth  to  the  first 
magnitude,  and  among  the  stars  of  this  class  has  attained  to 
the  brilliancy  of  Canopus,  and  almost  to  that  of  Sirius.  Sup- 
posing that  our  own  sun  has  passed  through  only  a  very  few 
of  these  variations  in  intensity  of  light  and  heat,  either  in  an 
increasing  or  decreasing  ratio  (and  why  should  it  differ  from 
other  suns  ?),  such  a  change,  such  a  weakening  or  augment- 

*  Observations  at  the  Cape,  $  259,  note  260. 

t  Heis,  in  his  Manuscript  Notices  of  May,  1 850  ;  also  Observations  at 
the  Cape,  p.  325 ;  and  P.  von  Boguslawski,  Uranus  for  1848,  p.  186. 
The  asserted  variation  of  n,  a,  and  6  Ursse  majoris  is  also  confirmed  in 
Outlines,  p.  559.  See  Madler,  Astr.,  p.  432.  On  the  succession  of  the 
stars  which,  from  their  proximity,  will  in  time  mark  the  north  pole, 
until,  after  the  lapse  of  12,000  years,  Vega,  the  brightest  of  all  possible 
polar  stars,  will  take  their  place.  ;  Vide  supra,  p.  96 

$  William  Herschel,  On  the  Changes  that  happen  to  the  Fixed  Stars, 
in  the  Philos.  Transact,  for  1796,  p.  186.  Sir  John  Herschel,  in  the 
Observations  at  the  Cape,  p.  350-352 ;  as  also  in  Mrs.  Somerviue's  ex- 
cellent work,  Connection  of  the  Physical  Sciences,  1846,  p.  407. 


182  COSMOS. 

ation  of  its  light-process,  may  account  for  far  greater  and 
more  fearful  results  for  our  own  planet  than  any  required  for 
the  explanation  of  all  geognostic  relations  and  ancient  telluric 
revolutions.  William  Herschel  and  Laplace  were  the  first 
to  agitate  these  views.  If  I  have  dwelt  upon  them  some- 
what at  length,  it  is  not  because  I  would  seek  exclusively  in 
these  the  solution  of  the  great  problem  of  the  changes  of 
temperature  in  our  earth.  The  primitive  high  temperature 
of  this  planet  at  its  formation,  and  the  solidification  of  con- 
glomerating matter  ;  the  radiation  of  heat  from  the  deeper 
strata  of  the  earth  through  open  fissures  and  through  unfilled 
veins  ;  the  greater  power  of  electric  currents  ;  a  very  differ- 
ent distribution  of  sea  and  land,  may  also,  in  the  earliest 
epochs  of  the  earth's  existence,  have  rendered  the  diffusion 
of  heat  independent  of  latitude  ;  that  is  to  say,  of  position 
relatively  to  a  central  body.  Cosmical  considerations  must 
not  be  limited  merely  to  astrognostic  relations. 


V. 

PROPER  MOTION  OF  THE  FIXED  STARS.  —  PROBLEMATICAL  EXIST- 
ENCE OF  DARK  COSMICAL  BODIES.—  PARALLAX—  MEASURED  DIS- 
TANCES OF  SOME  OF  THE  FIXED  STARS.—  DOUBTS  AS  TO  THE  AS- 
SUMPTION OF  A  CENTRAL  BODY  FOR  THE  WHOLE  SIDEREAL  HEAV- 
ENS. 

THE  heaven  of  the  fixed  stars,  in  contradiction  to  its  very 
name,  exhibits  not  only  changes  in  the  intensity  of  light,  but 
also  further  variation  from  the  perpetual  motion  of  the  indi- 
vidual stars.  Allusion  has  already  been  made  to  the  fact 
that,  without  disturbing  the  equilibrium  of  the  star-systems, 
no  fixed  point  is  to  be  found  in  the  whole  heavens,  and  that 
of  all  the  bright  stars  observed  by  the  earliest  of  the  Greek 
astronomers,  not  one  has  kept  its  place  unchanged.  In  the 
case  of  Arcturus,  of/z  Cassiopeise,  and  of  a  double  star  in  Cyg- 
nus,  this  change  of  position  has,  by  the  accumulation  of  their 
annual  proper  motion  during  2000  years,  amounted  respect- 
ively to  2|,  3i,  and  6  moon's  diameters.  In  the  course  of 
3000  years  about  twenty  fixed  stars  will  have  changed  their 
places  by  1°  and  upward.*  Since  the  proper  motions  of  the 
fixed  stars  rise  from  •£$th  of  a  second  to  7-7  seconds  (and 


*  Encke,  Betrachtungen  fiber  die  Anordnung  des  Stern-systems,  B.  12. 
Vidctupra,  p.  27.    Madler,  Astr.,  s.  445. 


PROPER    MOTION    OF  THE    STARS.  183 

consequently  differ,  at  the  least,  in  the  ratio  of  1 : 154),  the 
relative  distances  also  of  the  fixed  stars  from  each  other,  and 
the  configuration  of  the  constellations  themselves,  can  not  in 
long  periods  remain  the  same.  The  Southern  Cross  will  not 
always  shine  in  the  heavens  exactly  in  its  present  form,  for 
the  four  stars  of  which  it  consists  move  with  unequal  veloc- 
ity in  different  paths.  How  many  thousand  years  will  elapse 
before  its  total  dissolution  can  not  be  calculated.  In  the  re- 
lations of  space  and  the  duration  of  time,  no  absolute  idea 
can  be  attached  to  the  terms  great  and  small. 

In  order  to  comprehend  under  one  general  point  of  view 
the  changes  that  take  place  in  the  heavens,  and  all  the  mod- 
ifications which  in  the  course  of  centuries  occur  in  the  phys- 
iognomic character  of  the  vault  of  heaven,  or  in  the  aspect 
of  the  firmament  from  any  particular  spot,  we  must  reckon 
as  the  active  causes  of  this  change:  (1),  the  precession  of 
the  equinoxes  and  the  mutation  of  the  earth's  axis,  by  the 
combined  operation  of  which  new  stars  appear  above  the 
horizon,  and  others  become  invisible  ;  (2),  the  periodical  and 
non-periodical  variations  in  the  brightness  of  many  of  the 
fixed  stars ;  (3),  the  sudden  appearance  of  new  stars,  of 
which  a  few  have  continued  to  shine  in  the  heavens  ;  (4), 
the  revolution  of  telescopic  double  stars  round  a  common 
center  of  gravity.  Among  these  so-called  fixed  stars,  which 
change  slowly  and  unequally  both  in  the  intensity  of  their 
light  and  in  their  position,  twenty  principal  planets  move  in 
a  more  rapid  course,  five  of  them  being  accompanied  by 
twenty  satellites.  Besides  the  innumerable,  but  undoubt- 
edly rotatory  fixed  stars,  forty  moving  planetary  bodies  have 
up  to  this  time  (October,  1850)  been  discovered.  In  the 
time  of  Copernicus  and  of  Tycho  Brahe,  the  great  improver 
of  the  science  of  observation,  only  seven  were  known.  Near- 
ly two  hundred  comets,  five  of  which  have  short  periods  of 
revolution  and  are  interior,  or,  in  other  words,  are  inclosed 
within  those  of  the  principal  planets,  still  remain  to  be  men- 
tioned in  our  list  of  planetary  bodies.  Next  to  the  actual 
planets  and  the  new  cosmical  bodies  which  shine  forth  sud- 
denly as  stars  of  the  first  magnitude,  the  comets,  when,  dur- 
ing their  usually  brief  appearance  they  are  visible  to  the  na 
ked  eye,  contribute  the  most  vivid  animation  to  the  rich^'c- 
ture — I  had  almost  said  the  impressive  landscape — of  the 
starry  heavens. 

The  knowledge  of  the  proper  motion  of  the  fixed  stars  is 
closely  connected  historically  with  the  progress  of  the  sci- 


184  COSMOS. 

ence  of  observation  through  the  improvement  of  instruments 
and  methods.  The  discovery  of  this  motion  was  first  ren- 
dered practicable  when  the  telescope  was  combined  with 
graduated  instruments  ;  when,  from  the  accuracy  of  within 
a  minute  of  an  arc  (which  after  much  pains  Tycho  Brahe 
first  succeeded  in  giving  to  his  observations  on  the  island  of 
Hven),  astronomers  gradually  advanced  to  the  accuracy  of 
a  second  and  the  parts  of  a  second ;  and  when  it  became 
possible  to  compare  with  one  another  results  separated  by  a 
long  series  of  years.  Such  a  comparison  was  made  by  Hal- 
ley  with  respect  to  the  positions  of  Sirius,  Arcturus,  and  Al- 
debaran,  as  determined  by  Ptolemy  in  his  Hipparchian  cat- 
alogue, 1844  years  before.  By  this  comparison  he  consid- 
ered himself  justified  (1717)  in  announcing  the  fact  of  a 
proper  motion  in  the  three  above-named  fixed  stars.*  The 
high  and  well-merited  attention  which,  long  subsequent  even 
to  the  observations  of  Flamstead  and  Bradley,  was  paid  to 
the  table  of  right  ascensions  contained  in  the  Triduum  of 
Romer,  stimulated  Tobias  Mayer  (1756),  Maskelyne  (1770), 
and  P;azzi  (1800)  to  compare  Homer's  observations  with 
more  recent  ones.f  The  proper  motion  of  the  stars  was  in 
some  degree  recognized  as  a  general  fact,  even  in  the  mid 
die  of  the  last  century  ;  but  for  the  more  precise  and  numer- 
ical determination  of  this  class  of  phenomena  we  are  in- 
debted to  the  great  work  of  William  Herschel  in  1783,  found- 
ed on  the  observations  of  Flamstead,  $  and  still  more  to  Bes- 
sel  and  Argelander's  successful  comparison  of  Bradley's  "Po- 
sitions of  the  Stars  for  1755"  with  recent  catalogues. 

The  discovery  of  the  proper  motion  of  the  fixed  stars  has 
proved  of  so  much  the  greater  importance  to  physical  astron- 
omy, as  it  has  led  to  a  knowledge  of  the  motion  of  our  own 
solar  system  through  the  star-filled  realms  of  space,  and,  in- 
deed, to  an  accurate  knowledge  of  the  direction  of  this  mo- 
tion. We  should  never  have  become  acquainted  with  this 
fact  if  the  proper  progressive  motion  of  the  fixed  stars  were 
so  small  as  to  elude  all  our  measurements.  The  zealous  at- 
tempts to  investigate  this  motion,  both  in  its  quantity  and 
its  direction,  to  determine  the  parallax  of  the  fixed  stars,  and 

*  Halley,  in  the  Philos.  Transact,  for  1717-1719,  vol.  xxx..  p.  736. 
The  essay,  however,  referred  solely  to  variations  in  latitude.  Jacques 
Cassini  was  the  first  to  add  variations  in  longitude.  (Arago,  ii  the  An- 
Huairepour  1842,  p.  387.) 

t  Delambre,  Hist,  de  V Aslron.  Moderne,  t.  ii.,  p.  658.  Als  ,  «  £f& 
de  VAstron.  au  IMme  Slide,  p.  448. 

t  Philos.  Transact.,  vol.  Ixxiii.,  p.  138. 


PROPER  MOTION  OP  THE  STARS.         185 

their  distances,  have,  by  leading  to  the  improvement  and 
perfection  of  arc-graduation  and  optical  instruments  in  con- 
nection with  micrometric  appliances,  contributed  more  than 
any  thing  else  to  raise  the  science  of  observation  to  the 
height  which,  by  the  ingenious  employment  of  great  merid- 
ian-circles, refractors,  and  heliometers,  it  has  attained,  espe- 
cially since  the  year  1830. 

The  quantity  of  the  measured  proper  motions  of  the  stars 
varies,  as  we  intimated  at  the  commencement  of  the  present 
section,  from  the  twentieth  part  of  a  second  almost  to  eight 
seconds.  The  more  luminous  stars  have  in  general  a  slower 
motion  than  stars  from  the  fifth  to  the  sixth  and  seventh  mag- 
nitudes.* Seven  stars  have  revealed  an  unusually  great 
motion,  namely  :  Arcturus,  first  magnitude  (2"- 25) ;  a  Cen- 
tauri,  first  magnitude  (3//-58)  ;t  ft  Cassiopeia?,  sixth  magni- 
tude (3"-74) ;  the  double  star,  6  Eridani,  5'4  magnitude 
(4"-08) ;  the  double  star  61  Cygni,  5'6  magnitude  (5"'123), 
discovered  by  Bessel  in  1812,  by  means  of  a  comparison  with 
Bradley 's  observations  ;  a  star  in  the  confines  of  the  Canes 
Venatici,J  and  the  Great  Bear,  No.  1830  of  the  catalogue  of 
the  circumpolar  stars  by  Groombridge,  seventh  magnitude 
(according  to  Argelander,  6"-974) ;  e  Indi  (7"'74,  according 
to  D'Ariest)  ;§  2151  Puppis,  sixth  magnitude  (7"-&7l).  The 
uilihrn-oiicalll  mean  of  the  several  proper  motions  of  the  fixed 
stars  in  all  the  zones  into  which  the  sidereal  sphere  has  been 
divided  by  Madler  would  scarcely  exceed  0"'102. 

An  important  inquiry  into  the  "  Variability  of  the  proper 
motions  of  Procyon  and  Sirius,"  in  the  year  1844,  a  short 

*  Bessel,  in  the  Jahrbuch  wn  Schumacher  fur  1839,  s.  38.  Arago 
Annuaire  pour  1842,  p.  389. 

t  a  Centauri,  see  Henderson  and  Maclear,  in  the  Memoirs  of  the 
Astron.  Soc.,  vol.  xi.,  p.  61  ;  and  Piazzi  Smyth,  in  the  Edinburgh 
Transact.,  vol.  xvi.,  p.  447.  The  proper  motion  of  Arcturus,  2"-25 
(Daily,  in  the  same  Memoirs,  vol.  v.,  p.  165),  considered  as  that  of  a 
very  bright  star,  may  be  called  very  large  in  comparison  with  Aldeba 
ran,  0"-185  (Madler,  CentraUonne,  a.  11),  and  o  Lyra,  0"-400.  Among 
the  stars  of  the  first  magnitude,  a  Centauri,  with  its  great  proper  motion 
of  3"-58,  firms  a  very  remarkable  exception.  The  proper  motion  of 
the  binary  system  of  Cygnus  amounts,  according  to  Bessel  (Schum 
Astr.  Nochr.,  bd.  xvi.,  s.  93),  to  5"-123. 

{  Schumacher's  Astr.  Nochr.,  No.  455. 

$  Op.  cit.,  No.  618,  s.  276.  D'Arest  founds  this  result  on  comparisons 
of  LacaiDe  (1750)  with  Brisbane  (1825),  and  of  Brisbane  with  Taylor 
(1835).  The  star  2151,  Puppis,  has  a  proper  motion  of  7"-871,  and  ia 
of  the  sixth  magnitude.  (Maclear,  in  Madler's  Unlert.  uber  die  Fix- 
ttern-Sytteme,  th.  ii.,  s.  5.) 

||  Schum.,  Aslr  Nochr.,  No.  661,  s.  201 


186  COSMOS. 

time,  therefore,  before  the  beginning  of  his  last  and  painful 
illness,  led  Bessel,  the  greatest  astronomer  of  our  time,  to  the 
conviction  "  that  stars  whose  variable  motion  becomes  appar- 
ent by  means  of  the  most  perfect  instruments,  are  parts  of 
systems  confined  to  very  limited  spaces  in  proportion  to  their 
great  distances  from  one  another."  This  belief  in  the  exist- 
ence of  double  stars,  one  of  which  is  devoid  of  light,  was  so 
firmly  fixed  in  Bessel's  mind,  as  my  long  correspondence  with 
him  testifies,  that  it  excited  the  most  universal  attention, 
partly  on  his  account,  and  partly  from  the  great  interest 
which  independently  attaches  itself  to  every  enlargement  of 
our  knowledge  of  the  physical  constitution  of  the  sidereal 
heavens.  "  The  attracting  body,"  this  celebrated  observer 
remarked,  "  must  be  very  near  either  to  the  fixed  star  which 
reveals  the  observed  change  of  position,  or  to  the  sun.  As, 
however,  the  presence  of  no  attracting  body  of  considerable 
mass  at  a  very  small  distance  from  the  sun  has  yet  been  per- 
ceived in  the  motions  of  our  own  planetary  system,  we  are 
brought  back  to  the  supposition  of  its  very  small  distance 
from  a  star,  as  the  only  tenable  explanation  of  that  change 
in  the  proper  motion  which,  in  the  course  of  a  century,  be- 
comes appreciable."*  In  a  letter  (dated  July,  1844)  in  an- 
swer to  one  in  which  I  had  jocularly  expressed  my  anxiety 
regarding  the  spectral  world  of  dark  stars,  he  writes :  "At 
all  events,  I  continue  in  the  belief  that  Procyon  and  Sirius 
are  true  double  stars,  consisting  of  a  visible  and  an  invisible 
star.  No  reason  exists  for  considering  luminosity  an  essen- 
tial property  of  these  bodies.  The  fact  that  numberless  stars 
are  visible  is  evidently  no  proof  against  the  existence  of  an 
equally  incalculable  number  of  invisible  ones.  The  physical 
difficulty  of  a  change  in  the  proper  motion  is  satisfactorily 
set  aside  by  the  hypothesis  of  dark  stars.  No  blame  attaches 
to  the  simple  supposition  that  the  change  of  velocity  only 
takes  place  in  consequence  of  the  action  of  a  force,  and  that 
forces  act  in  obedience  to  the  Newtonian  laws." 

A  year  after  Bessel's  death,  Fuss,  at  Struve's  suggestion, 
renewed  the  investigation  of  the  anomalies  of  Procyon  and 
Sirius,  partly  with  new  observations  with  Ertel's  meridian- 
telescope  at  Pulkowa,  and  partly  with  reductions  of,  and  com- 
parisons with,  earlier  observations.  The  result,  in  the  opin- 
ion of  Struve  and  Fuss,t  proved  adverse  to  Bessel's  assertion. 

*  Schuin.,  Attr.  Nachr.,  Nos.  514-516. 

t  Struve,  Etudes  cCAstr.  Stellaire,  Texte,  p.  47,  Notes,  p.  26,  and  51- 
57 ;  Sir  John  Herschel,  Outl.,  $  859  and  860. 


PROPER   MOTION    OP  THE    STARS.  187 

A.  laborious  investigation  which  Peters  has  now  completed 
at  Konigsberg,  on  the  other  hand,  justifies  it ;  as  does  also  a 
similar  one  advanced  by  Schubert,  the  calculator  for  the 
North  American  Nautical  Almanac. 

The  belief  in  the  existence  of  non-luminous  stars  was  dif- 
fused even  among  the  ancient  Greeks,  and  especially  in  the 
earliest  ages  of  Christianity.  It  was  assumed  that  among 
the  fiery  stars  which  are  nourished  by  the  celestial  vapcrs, 
there  revolve  certain  other  earth-like  bodies,  which,  however, 
remain  invisible  to  us."*  The  total  extinction  of  new  stars, 
especially  of  those  so  carefully  observed  by  Tycho  Brahe  and 
Kepler  in  Cassiopeia  and  Ophiuchus,  appears  to  corroborate 
this  opinion.  Since  it  was  at  the  time  conjectured  that  the 
first  of  these  stars  had  already  twice  appeared,  and  that,  too, 
at  intervals  of  nearly  300  years,  the  idea  of  annihilation 
and  total  extinction  naturally  gained  little  or  no  credit.  The 
immortal  author  of  the  Mecanique  Celeste  bases  his  convic- 
tion of  the  existence  of  non-luminous  masses  in  the  universe 
on  these  same  phenomena  of  1572  and  1604  :  "  These  stars, 
that  have  become  invisible  after  having  surpassed  the  brill- 
iancy of  Jupiter,  have  not  changed  their  place  during  the 
time  of  their  being  visible."  (The  luminous  process  in  them 
has  simply  ceased.)  "  There  exist,  therefore,  in  celestial 
space  dark  bodies  of  equal  magnitudes,  and  probably  in  as 
great  numbers  as  the  stars,  "t  So  also  Madler,  in  his  Un- 
tersuchungen  uber  die  Fixstern-Systeme,  says  :J  "A  dark 
body  might  be  a  central  body  ;  it  might,  like  our  own  sun, 
be  surrounded  in  its  immediate  neighborhood  only  by  dark 
bodies  like  our  planets.  The  motions  of  Sirius  and  Procyon, 
pointed  out  by  Bessel,  force  us  to  the  assumption  that  there 
are  cases  where  luminous  bodies  form  the  satellites  of  dark 
masses. "§  It  has  been  already  remarked  that  the  advocates 
of  the  emanation  theory  consider  these  masses  as  both  invis- 
ible, and  also  as  radiating  light :  invisible,  since  they  are  of 
such  huge  dimensions  that  the  rays  of  light  emitted  by  them 
(the  molecules  of  light),  being  impeded  by  the  force  of  at- 
traction, are  unable  to  pass  beyond  a  certain  limit.  H  If,  as 

*  Origen,  in  Gronov.  Thesaur.,  t.  x.,  p.  271. 

t  Laplace,  Expos,  du  Syst.  du  Monde,  1824,  p.  395.  Lambert,  in  his 
Kosmologische  Brief e,  shows  remarkable  tendency  to  adopt  the  hypoth- 
esis  of  large  dark  bodies. 

•      \  Madler,  Untersitch.  tober  die  Fixstern-Systeme,  th.  ii.  (1848),  s.  3; 
and  his  Astronomy,  B.  416.  $  Vide  note  t,  p.  186 

II  Vide  supra,  p.  88,  and  note ;  Laplace,  in  Zach's  Alia.  Geogr 
Epkcm.,  bd.  iv.,  B.  1 ;  Madler,  Astr.,  B.  393. 


188  COSMOS. 

may  well  be  assumed,  there  exist,  in  the  regions  of  space, 
dark  invisible  bodies  in  which  the  process  of  light-producing 
vibration  does  not  take  place,  these  dark  bodies  can  not  fall 
within  the  sphere  of  our  own  planetary  and  cometary  system, 
or,  at  all  events,  their  mass  can  only  be  very  small,  since 
their  existence  is  not  revealed  to  us  by  any  appreciable  dis- 
turbances. 

The  inquiry  into  the  quality  and  direction  of  the  motion  of 
the  fixed  stars  (both  of  the  true  motion  proper  to  them,  and 
also  of  their  apparent  motion,  produced  by  the  change  in 
the  place  of  observation,  as  the  earth  moves  in  its  orbit),  the 
determination  of  the  distances  of  the  fixed  stars  from  the 
sun  by  ascertaining  their  parallax,  and  the  conjecture  as  to 
the  part  in  universal  space  toward  which  our  planetary 
system  is  moving,  are  three  problems  in  astronomy  which, 
through  the  means  of  observation  already  successfully  em- 
ployed in  their  partial  solution,  are  closely  connected  with 
each  other.  Every  improvement  in  the  instruments  and 
methods  which  have  been  used  for  the  furtherance  of  any 
one  of  these  difficult  and  complicated  problems  has  been 
beneficial  to  the  others.  I  prefer  commencing  with  the  par- 
allaxes and  the  determination  of  the  distances  of  certain  fixed 
stars,  to  complete  that  which  especially  relates  to  our  pres 
ent  knowledge  of  isolated  fixed  stars. 

As  early  as  the  beginning  of  the  seventeenth  century, 
Galileo  had  suggested  the  idea  of  measuring  the  "  certainly 
very  unequal  distances  of  the  fixed  stars  from  the  solar  sys- 
tem," and,  indeed,  with  great  ingenuity,  was  the  first  to 
point  out  the  means  of  discovering  the  parallax  ;  not  by  de- 
termining the  star's  distance  from  the  zenith  or  the  pole,  "but 
by  the  careful  comparison  of  one  star  with  another  very  near 
it."  He  gives,  in  very  general  terms,  an  account  of  the  mi- 
crometrical  method  which  William  Herschel  (1781),  Struve, 
and  Bessel  subsequently  made  use  of.  "  Perche  io  non  credo," 
says  Galileo,*  in  his  third  dialogue  (Giornata  terza),  "  che 
tutte  le  stella  siano  sparse  in  una  sferica  superficie  egual- 
tnente  distanti  da  un  centra;  ma  stimo,  che  le  loro  lonta- 
nanze  da  noi  siano  talmente  varie,  che  alcune  ve  ne  possano 
esser  2  e  3  volte  piu  remote  di  alcune  altre  ;  talche  quando 
si  trovasse  col  telescopic  qualche  picciolissima  Stella  vici- 

*  Opere  di  Galileo  Galilei,  vol.  xii.,  Milano,  1811,  p.  206.  This  re- 
markable  passage,  which  expresses  the  possibility  and  the  project  of 
a  measurement,  was  pointed  out  by  Arago ;  see  his  Annuaire  pour  1842 
p.  382. 


DISTANCES  OF  THE  STARS.  189 

nissima  ad  alcuna  delle  maggiori,  e  che  pero  quella  fussc  al- 
tissima,  potrebbe  accadere  che  qualche  sensibil  mutazione 
succedes&e  tra  di  loro."  "  \\Ther6fore  I  do  not  believe."  says 
Galileo,  in  liis  third  discourse  (Giornata  terza),  <:that  all  the 
stars  are  scattered  over  a  spherical  superficies  at  equal  dis- 
tances from  a  common  center  ;  but  I  am  of  opinion  that  their 
distances  from  us  are  so  various  that  some  of  them  may  be 
two  or  three  times  as  remote  as  others,  so  that  when  some 
minute  star  is  discovered  by  the  telescope  close  to  one  of  the 
larger,  and  yet  the  former  is  highest,  it  may  be  that  some 
sensible  change  might  take  place  among  them."  The  in- 
troduction of  the  Copernican  system  imposed,  as  it  were,  the 
necessity  of  numerically  determining,  by  means  of  measure- 
ment, the  change  of  direction  occasioned  in  the  position  of 
the  fixed  stars  by  the  earth's  semi-annual  change  of  place  in 
its  course  round  the  sun.  Tycho  Brahe's  angular  determina- 
tions, of  which  Kepler  so  successfully  availed  himself,  do  not 
manifest  any  perceptible  change  arising  from  parallax  in 
the  apparent  positions  of  the  fixed  stars,  although,  as  I  have 
already  stated,  they  are  accurate  to  a  minute  of  the  arc. 
For  this  the  Copernicans  long  consoled  themselves  with  the 
reflection  that  the  diameter  of  the  earth's  orbit  (165£  mill- 
ions of  geographical  miles)  was  insignificant  when  compared 
to  the  immense  distance  of  the  fixed  stars. 

The  hope  of  being  able  to  determine  the  existence  of  par- 
allax must  accordingly  have  been  regarded  as  dependent  on 
the  perfection  of  optical  and  measuring  instruments,  and  on 
the  possibility  of  accurately  measuring  -very  small  angles. 
As  long  as  such  accuracy  was  only  secure  within  a  minute, 
the  non-observance  of  parallax  merely  testified  to  the  fact 
that  the  distance  of  the  fixed  stars  must  be  more  than  3438 
times  the  earth's  mean  distance  from  the  sun,  or  semi-di- 
ameter of  its  orbit.*  This  lower  limit  of  distances  rose  to 
206,265  semi-diameters  when  certainty  to  a  second  was  at- 
tained in  the  observations  of  the  great  astronomer,  James 
Bradley  ;  and  in  the  brilliant  period  of  Frauenhofer's  instru- 
ments (by  the  direct  measurement  of  about  the  tenth  part 
of  a  second  of  arc),  it  rose  still  higher,  to  2,062,648  mean 
distances  of  the  earth.  The  labors  and  the  ingeniously  con- 
trived zenith  apparatus  of  Newton's  great  cotemporary ,  Rob- 
ert Hooke  (1669),  did  not  lead  to  the  desired  end.  Picard, 
Horrebow  (who  worked  out  Romer's  rescued  observations) 

*  Bessel,  in  Schumacher's  Jahrb.  fur  1839,  s.  511. 


190  COSMOS 

and  Flamstead  believed  that  they  had  discovered  parallaxes 
of  several  seconds,  whereas  they  had  confounded  the  proper 
motions  of  the  stars  with  the  true  changes  from  parallax. 
On  the  other  hand,  the  ingenious  John  Michell  (Phil.  Trans. 
1767,  vol.  Ivii.,  p.  234-264)  was  of  opinion  that  the  paral- 
laxes of  the  nearest  fixed  stars  must  be  less  than  0"'02,  and 
in  that  case  could  only  "become  perceptible  when  magnified 
12,000  times."  In  consequence  of  the  widely-diffused  opin- 
ion, that  the  superior  brilliancy  of  a  star  must  invariably  in- 
dicate a  greater  proximity,  stars  of  the  first  magnitude,  as, 
for  instance,  Vega,  Aldebaran,  Sirius,  and  Procyon,  were, 
with  little  success,  selected  for  observation  by  Calandrelli 
and  the  meritorious  Piazzi  (1805).  These  observations  must 
be  classed  with  Jhose  which  Brinkley  published  in  Dublin 
(1815),  and  which,  ten  years  afterward,  were  refuted  by 
Pond,  and  especially  by  Airy.  An  accurate  and  satisfactory 
knowledge  of  parallaxes,  founded  on  micrometric  measure- 
ments, dates  only  from  between  the  years  1832  and  1838 

Although  Peters,*  in  his  valuable  work  on  the  distance? 
of  the  fixed  stars  (1846),  estimates  the  number  of  parallaxes 
hitherto  discovered  at  33,  we  shall  content  ourselves  with  re 
ferring  to  9,  which  deserve  greater,  although  very  different, 
degrees  of  confidence,  and  which  we  shall  consider  in  the 
probable  order  of  their  determinations. 

The  first  place  is  due  to  the  star  61  Cygni,  which  Bessel 
has  rendered  so  celebrated.  The  astronomer  of  Kbnigsberg 
determined,  in  1812,  the  large  proper  motion  of  this  double 
star  (below  the  sixth  magnitude),  but  it  was  not  until  1838 
that,  by  means  of  the  heliometer,  he  discovered  its  parallax. 
Between  the  months  of  August,  1812,  and  November,  1813, 
my  friends  Arago  and  Mathieu  instituted  a  series  of  numer- 
ous observations  for  the  purpose  of  finding  the  parallax  of 
the  star  61  Cygni,  by  measuring  its  distance  from  the  zenith. 
In  the  course  of  their  labors  they  arrived  at  the  very  correct 
conclusion  that  the  parallax  of  this  star  was  less  than  half  a 
second.f  So  late  as  1815  and  1816,  Bessel,  to  use  his  own 

*  Struve,  Astr.  Slell.,  p.  104. 

t  Arago,  in  the  Connaissance  des  Temps  pour  1834,  p.  281 :  "  Nous 
observames  avec  beaucoap  de  soin,  M.  Mathieu  et  moi,  pendant  le 
mois  d'Aout,  1812.  et  pendant  le  mois  de  Novembre  suivant,  In  hauteur 
angulaire  de  l'4toile  audessus  de  1'horizon  de  Paris.  Cette  hauteur,  & 
la  seconde  <§poque,  ne  surpasse  la  hauteur  angulaire  a  la  premiere  quo 
de  0"-66.  Une  parallaxe  absolue  d'une  seule  seconde  aurait  n&sessairo- 
raent  amend  entre  ces  deux  hauteurs  une  difference  de  l"-2.  Nos  ob- 
servations u'indiqueut  douc  pas  quo  le  rayon  de  1'orbite  terreste,  que 


DISTANCES  OF  THE  STARS.  191 

words,  "  had  arrived  at  no  available  result."*  The  observa- 
tions taken  from  August,  1837,  to  October,  1838,  by  means 
of  the  great  heliometer  erected  in  1829,  first  led  him  to  the 
parallax  of  0"-3483,  which  corresponds  with  a  distance  of 
592,200  mean  distances  of  the  earth,  and  a  period  of  9| 
years  for  the  transmission  of  its  light.  Peters  confirmed  this 
result  in  1842  by  finding  0"'3490,  but  subsequently  changed 
Bessel's  result  into  0"-3744  by  a  correction  for  temperature. 1 
The  parallax  of  the  finest  double  star  of  the  southern  hem- 
isphere (a  Centauri)  has  been  calculated  at  0"'9128  by  the 
observations  of  Henderson,  at  the  Cape  of  Good  Hope,  in 

39  millions  de  lieues  soient  vus  de  la  61"  du  Cygne  sous  un  angle  de 
plus  d'une  demi-seconde.  Mais  une  base  vue  perpendiculairement  sou- 
tend  un  angle  d'une  demi-seconde  quand  on  est  eloigne  de  412  mille 
fois  sa  longueur.  Done  la  61e  du  Cygne  est  au  moins  a  une  distance 
de  la  terre  egale  a  412  mille  fois  39  millions  de  lieues."  "  During  the 
month  of  August,  1812,  and  also  during  the  following  November,  Mr. 
Mathieu  and  myself  very  carefully  observed  the  altitude  of  the  star 
above  the  horizon,  at  Paris.  At  the  latter  period  its  altitude  only  ex- 
ceeded that  of  the  former  by  0"-66.  An  absolute  parallax  of  only  a 
single  second  would  necessarily  have  occasioned  a  difference  of  l"-2 
between  these  heights.  Our  observations  do  not,  therefore,  show  that 
a  semi-diameter  of  the  earth's  orbit,  or  thirty-nine  millions  of  leagues, 
are  seeu  from  the  star  61  of  Cygnus,  at  an  angle  of  more  than  0"-5. 
But  a  base  viewed  perpendicularly  subtends  an  angle  of  0"'5  only  when 
it  is  observed  at  a  distance  of  412,000  times  its  length.  Therefore  the 
star  6 1  Cygni  is  situated  at  a  distance  from  our  earth  at  least  equal  to  four 
hundred  and  twelve  thousand  times  thirty-nine  millions  of  leagues." 

*  Bessel,  in  Schum.,  Jahrb.  1839,  s.  39-49,  and  in  the  Astr.  Nachr., 
No.  366,  gave  the  result  0"-3136  as  a  first  approximation.  His  later  and 
final  result  was  0"-3483.  (Astr.  Nachr.,  No.  402,  in  bd.  xvii.,  s.  274.) 
Peters  obtained  by  his  own  observations  the  following,  almost  identical, 
result  of  0"-3490.  (Struve,  Astr.  Slell,  p.  99.)  The  alteration  which, 
after  Bessel's  death,  was  made  by  Peters  in  Bessel's  calculations  of  the 
angular  measurements,  obtained  by  the  Konigsberg  heliometer,  arises 
from  the  circumstance  that  Bessel  expressed  his  intention  (Astr.  Nachr., 
bd.  xvii.,  s.  267)  of  investigating  further  the  influence  of  temperature 
on  the  results  exhibited  by  the  heliometer.  This  purpose  he  had,  in 
fact,  partially  fulfilled  in  the  first  volume  of  his  Astronomische  Untersuch- 
ungen,  but  he  had  not  applied  the  corrections  of  temperature  to  the  ob- 
servations of  parallax.  This  application  was  made  by  the  eminent  as- 
tronomer Peters  (Ergdnzungscheft  zu  den  Astr.  Nachr.,  1849,  s.  56), 
and  the  result  obtained,  owing  to  the  corrections  of  temperature,  was 
0"-3744  instead  of  0"-3483. 

t  This  result  of  0"-3744  gives,  according  to  Argelander,  as  the  dis- 
tance of  the  double  star  61  Cygni  from  the  sun,  550,900  mean  distances 
of  the  earth  from  the  sun,  or  45,576,000  miles,  a  distance  which  light 
traverses  in  3177  mean  days.  To  judge  from  the  three  consecutive 
statements  of  parallax  given  by  Bessel,  0"-3136,  0"-3483,  and  0"-3744, 
this  celebrated  double  star  has  apparently  come  gradually  nearer  to  us 
in  light  passages  amounting  respectively  to  10,  9\,  and  8T7ff  yeara 


192  COSMOS. 

1832,  and  by  those  of  Maclear  in  1839.*  According  to  this 
statement,  it  is  the  nearest  of  all  the  fixed  stars  that  have 
yet  been  measured,  being  three  times  nearer  than  61  Cygni. 

The  parallax  of  a  Lyrse  has  long  been  the  object  of 
Struve's  observations.  The  earlier  observations  (1836) 
gavet  between  0"-07  and  0"-18  ;  later  ones  gave  0"-2613, 
and  a  distance  of  771,400  mean  distances  of  the  earth,  with 
a  period  of  twelve  years  for  the  transmission  of  its  light. t 
But  Peters  found  the  distance  of  this  brilliant  star  to  be 
much  greater,  since  he  gives  only  0"'103  as  the  parallax. 
This  result  contrasts  with  another  star  of  the  first  magni- 
tude (a  Centauri),  and  one  of  the  sixth  (61  Cygni). 

The  parallax  of  the  Polar  Star  has  been  fixed  by  Peters 
at  0"*106,  after  many  comparisons  of  observations  made  be- 
tween the  years  1818  and  1838  ;  and  this  is  the  more  sat- 
isfactory, as  the  same  comparisons  give  the  aberration  at 
20"-455.§ 

The  parallax  of  Arcturus,  according  to  Peters,  is  0"-127. 
Riimker's  earlier  observations  with  the  Hamburg  meridian 
circle  had  made  it  considerably  larger.  The  parallax  of  an- 
other star  of  the  first  magnitude,  Capella,  is  still  less,  being, 
according  to  Peters,  0"'046. 

The  star  No.  1830  in  Groombridge's  Catalogue,  which, 
according  to  Argelander,  showed  the  largest  proper  motion 
of  all  the  stars  that  hitherto  have  been  observed  in  the  firm- 
ament, has  a  parallax  of  0"-226,  according  to  48  zenith 
distances  which  were  taken  with  much  accuracy  by  Peters 
during  the  years  1842  and  1843.  Faye  had  believed  it  to 
be  five  times  greater,  1"-08,  and  therefore  greater  than  the 
parallax  of  a  Centauri.  || 

*  Sir  John  Herschel,  Outlines,  p.  545  and  551.  Madler  (Astr.,  s.  425) 
gives  in  the  case  of  a  Centauri  the  parallax  0"-9213  instead  of  0"-9128. 

t  Struve  Stell.  compos.  Mens.  Microm.,  p.  clxix.-clxxii.  Airy  makes 
the  parallax  of  a  Lyrse,  which  Peters  had  previously  reduced  to  0"-1, 
still  lower;  indeed,  too  small  to  be  measurable  by  our  present  instru- 
ments. (Mem.  of  the  Royal  Astr.  Soc.,  vol.  x.,  p.  270.) 

J  Struve,  On  the  Micrometrical  Admeasurements  by  the  Great  Refract" 
or  at  Dorpat  (Oct.,  1839),  in  Schum.,  Astr.  Nachr.,  No.  396,  s.  178. 

$  Peters,  in  Struve,  Aitr.  Stell.,  p.  100.  II  Id.,  p.  101. 


DISTANCES    OF    THE   STARS. 


19  j 


Filed  Star. 

Parallax. 

ProtabEi 

Error. 

Name  of  Observer. 

a  Centauri  

0"-  913 

0"-070 

Henderson  and  Maclear. 

61  Cygni  

0"3744 

0"-020 

Bessel. 

Sirius      .     ....... 

0"-  230 

Henderson 

1830,  Groombridge. 
i  Ursse  Maj. 

0"-  226 
0"-  133 

0"-141 
0"-106 

Peters. 
Peters. 

Arcturus 

0"-  127 

0"073 

Peters. 

a  Lyras  

0"-  207 

0"-038 

Peters. 

Polaris  

0"-  106 

0"-012 

Peters. 

Capella  

0"-  046 

0"-200 

Peters. 

It  does  not  in  general  follow  from  the  results  hitherto  ob- 
tained that  the  brightest  stars  are  likewise  the  nearest  to  us. 
Although  the  parallax  of  a  Centauri  is  the  greatest  of  all  at 
present  known,  on  the  other  hand,  Vega  Lyrte,  Arcturus,  and 
especially  Capella,  have  parallaxes  from  three  to  eight  times 
less  than  a  star  of  the  sixth  magnitude  in  Cygnus.  More- 
over, the  two  stars  which  after  2151  Puppis  and  e  Indi  show 
the  most  rapid  proper  motion,  viz.,  the  star  just  mentioned 
in  the  Swan  (with  an  annual  motion  of  5"- 123),  and  No. 
1830  of  Groombridge,  which  in  France  is  called  Argelander's 
star  (with  an  annual  motion  of  6"- 974),  are  three  and  four 
times  more  distant  from  the  sun  than  a  Centauri,  which  has 
a  proper  motion  of  3" -58.  Their  volume,  mass,  intensity  of 
light,*  proper  motion,  and  distance  from  our  solar  system, 
stand  in  various  complicated  relations  to  each  other.  Al- 
though, therefore,  generally  speaking,  it  may  be  probable  that 
the  brightest  stars  are  nearest  to  us,  still  there  may  be  cer- 
tain special  very  remote  stars,  whose  photospheres  and  sur- 
faces, from  the  nature  of  their  physical  constitution,  maintain 
a  very  intense  luminous  process.  Stars  which  from  their 
brilliancy  we  reckon  to  be  of  the  first  magnitude,  may  be 
further  distant  from  us  than  others  of  the  fourth,  or  even  of 
the  sixth  magnitude.  When  we  pass  by  degrees  from  the 
consideration  of  the  great  starry  stratum  of  which  our  solar 
system  is  a  part,  to  the  particular  subordinate  systems  of  our 
planetary  world,  or  to  the  still  lower  systems  of  Jupiter's  and 
Saturn's  moons,  we  perceive  central  bodies  surrounded  by 
masses  in  which  the  successive  order  of  magnitude  and  of  in- 
tensity of  the  reflected  light  does  not  seem  to  depend  on  dis- 
tance. The  immediate  connection  subsisting  between  our 
still  imperfect  knowledge  of  parallaxes,  and  our  knowledge  of 

*  On  the  proportion  of  the  amount  of  proper  motion  to  the  proximity 
of  the  brighter  stars,  see  Struve,  Stell,  compot.  Mensuree  Aficrom.,  p 
clxi?. 

VOL.  Ill   -I 


194  COSMOS. 

the  whole  structural  configuration  of  the  universe,  lends  a  pe- 
culiar charm  to  those  investigations  which  relate  to  the  dis- 
tances of  the  fixed  stars. 

Human  ingenuity  has  invented  for  this  class  of  investiga- 
tions methods  totally  different  from  the  usual  ones,  and  which, 
being  based  on  the  velocity  of  light,  deserve  a  brief  mention 
in  this  place.  Savary,  whose  early  death  proved  such  a  loss 
to  the  physical  sciences,  had  pointed  out  how  the  aberration 
of  light  in  double  stars  might  be  used  for  determining  the 
parallaxes.  If,  for  instance,  the  plane  of  the  orbit  which  the 
secondary  star  describes  around  the  central  body  is  not  at 
right  angles  to  the  line  of  vision  from  the  earth  to  the  double 
star,  but  coincides  nearly  with  this  line  of  vision  itself,  then 
the  secondary  star  in  its  orbit  will  likewise  appear  to  describe 
nearly  a  straight  line,  and  the  points  in  that  portion  of  its 
orbit  which  is  turned  toward  the  earth  will  all  be  nearer  to 
the  observer  than  the  corresponding  points  of  the  second  half, 
which  is  turned  away  from  the  earth.  Such  a  division  into 
two  halves  produces  not  a  real,  but  an  apparent  unequal 
velocity,  with  which  the  satellite  in  its  orbit  recedes  from, 
or  approaches,  the  observer.  If  the  semi-diameter  of  this 
orbit  were  so  great  that  light  would  require  several  days  or 
weeks  to  traverse  it,  then  the  time  of  tlio  half  revolution 
through  its  more  remote  side  will  prove  to  be  longer  than  the 
time  in  the  side  turned  toward  the  observer.  The  sum  of 
the  two  unequal  times  will  always  be  equal  to  the  true  pe- 
riodic time ;  for  the  inequalities  caused  by  the  velocity  of  light 
reciprocally  destroy  each  other.  From  these  relations  of  du- 
ration, it  is  possible,  according  to  Savary's  ingenious  method 
of  changing  days  and  parts  of  days  into  a  standard  of  length 
(on  the  assumption  that  light  traverses  14,356  millions  of 
geographical  miles  in  twenty-four  hours),  to  arrive  at  the 
absolute  magnitude  of  a  semi-diameter  of  the  earth's  orbit , 
and  the  distance  of  the  central  body  and  its  parallax  may  be 
then  deduced  from  a  simple  determination  of  the  angle  under 
which  the  radius  appears  to  the  observer.* 

In  the  same  way  that  the  determination  of  the  parallaxes 
instructs  us  as  to  the  distances  of  a  small  number  of  the  fixed 
stars,  and  as  to  the  place  which  is  to  be  assigned  to  them  in 
the  regions  of  space,  so  the  knowledge  of  the  measure  and 
duration  of  proper  motion,  that  is  to  say,  of  the  changes  which 
take  place  in  the  positions  of  self-luminous  stars,,  throws  some 

*  Savary,  in  the  Connaissance  des  Temps  pour  1830,  p.  56-69,  and 
p.  163-171;  and  Struve,  ibid.,  D.  clxiv. 


PROPER    MOTION    OF    THE    STARS.  195 

light  on  two  mutually  dependent  problems ;  namely,  the  mo- 
tion of  the  solar  system,*  and  the  position  of  the  center  of 
gravity  in  the  heaven  of  the  fixed  stars.  That  which  can 
only  be  reduced  in  so  very  incomplete  a  manner  to  numerical 
relations,  must  for  that  very  reason  be  ill  calculated  to  throw 
any  clear  light  on  such  causal  connection.  Of  the  two  prob- 
lems just  mentioned,  the  first  alone  (especially  since  Arge- 
lander's  admirable  investigation)  admits  of  being  solved  with 
a  certain  degree  of  satisfactory  precision ;  the  latter  has  been 
considered  with  much  acuteness  by  Madler,  but,  according 
to  the  confession  of  this  astronomer  himself,  t  his  attempted 
solution  is,  in  consequence  of  the  many  mutually  compensa- 
ting forces  which  enter  into  it,  devoid  "  of  any  thing  like  evi- 
dence amounting  to  a  complete  and  scientifically  certain 
proof." 

After  carefully  allowing  for  all  that  is  due  to  the  preces- 
sion of  the  equinoxes,  the  nutation  of  the  earth's  axis,  the 
aberration  of  light,  and  the  change  of  parallax  caused  by  the 
earth's  revolution  round  the  sun,  the  remaining  annual  mo- 
tion of  the  fixed  stars  comprises  at  once  that  which  is  the 
consequence  of  the  translation  in  space  of  the  whole  sola? 
system,  and  that  also  which  is  the  result  of  the  actual  propel 
motion  -of  the  fixed  stars.  In  Bradley's  masterly  labors  on 
nutation,  contained  in  his  great  treatise  of  the  year  1748,  we 
meet  with  the  first  hint  of  a  translation  of  the  solar  system, 
and  in  a  certain  sense,  also,  with  suggestions  for  the  most 
desirable  methods  of  observing  it.J  "  For  if  our  own  solar 
system  be  conceived  to  change  its  place  with  respect  to  ab- 
solute space,  this  might,  in  process  of  time,  occasion  an  ap- 
parent change  in  the  angular  distances  of  the  fixed  stars  ; 
and  in  such  a  case,  the  places  of  the  nearest  stars  being  more 
affected  than  of  those  that  are  very  remote,  their  relative 
positions  might  seem  to  alter,  though  the  stars  themselves 
were  really  immovable.  And,  on  the  other  hand,  if  our  own 
system  be  at  rest,  and  any  of  the  stars  really  in  motion,  this 
might  likewise  vary  their  apparent  positions,  and  the  more 
so,  the  nearer  they  are  to  us,  or  the  swifter  their  motions  are, 
or  the  more  proper  the  direction  of  the  motion  is,  to  be  ren- 
dered perceptible  by  us.  Since,  then,  the  relative  places  of 

•  Cosmot,  vol.  i.,  p.  146.  t  Madler,  Astronomic,  B.  414. 

t  Arago,  in  his  Annuaire  pour  1842,  p.  383,  was  the  first  to  call  at- 
tention  to  this  remarkable  passage  of  Bradley's.  See,  in  the  same  An- 
nuaire, the  section  on  the  translation  of  the  entire  solar  system,  p.  389- 
399. 


i96  COSMOS. 

the  stars  may  be  changed  from  such  a  variety  of  causes,  con- 
sidering that  amazing  distance  at  which  it  is  certain  some 
of  them  are  placed,  it  may  require  the  observations  of  many 
ages  to  determine  the  laws  of  the  apparent  changes  even  of 
a  single  star ;  much  more  difficult,  therefore,  it  must  be  to 
settle  the  laws  relating  to  all  the  most  remarkable  stars." 

After  the  time  of  Bradley,  the  mere  possibility,  and  the 
greater  or  less  probability,  of  the  movement  of  the  solar  sys- 
tem, were  in  turn  advanced  in  the  writings  of  Tobias  Mayer, 
Lambert,  and  Lalande  ;  but  William  Herschel  had  the  great 
merit  of  being  the  first  to  verify  the  conj  ecture  by  actual  ob- 
servations (1783,  1805,  and  1806).  He  found  (what  has 
been  confirmed,  and  more  precisely  determined  by  many  later 
and  more  accurate  inquiries)  that  our  solar  system  moves  to- 
ward a  point  near  to  the  constellation  of  Hercules,  in  R.  A. 
260°  44',  and  N.  Decl.  26°  16'  (reduced  to  the  year  1800). 
Argelander,  by  a  comparison  of  3 1 9  stars,  and  with  a  refer- 
ence to  Lundahl's  investigations,  found  it  for  1800:  R.A. 
257°  54'-l,  Decl.  +28°  49'-2  ;  for  1850,  R.A.  258°  23'-5, 
Decl.  +28°  45'-6.  Otto  Struve  (from  392  stars)  made  it  to 
be  for  1800  :  R.  A.  261°  26'-9,  Decl.  +37°  35'-5  ;  for  1850, 
261°  52'-6,  Decl.  37°  33'-0.  According  to  Gauss,*  the  point 
in  question  falls  within  a  quadrangle,  whose  extremes  are, 
R.  A.  258°  40',  and  Decl.  30°  40' ;  R.  A.  258°  42',  Decl. 
+30°  57';  R.A.  259°  13',  Decl.  +31°  9';  R.A.  260°  4', 
Decl.  +30°  32'. 

It  still  remained  to  inquire  what  the  result  would  be  if 
the  observations  were  directed  only  to  those  stars  of  the  south- 
ern hemisphere  which  never  appear  above  the  horizon  in  Eu- 
rope. To  this  inquiry  Galloway  has  devoted  his  especial 
attention.  He  has  compared  the  very  recent  calculations 
(1830)  of  Johnson  at  St.  Helena,  and  of  Henderson  at  the 
Cape  of  Good  Hope,  with  the  earlier  ones  of  Lacaille  and 
Bradley  (1750  and  1757).  The  result!  for  1790  was  R.  A. 
260°  0',  Decl.  34°  23' ;  therefore,  for  1800  and  1850,  260° 
5',  +  34°  22',  and  260°  33',  +  34°  20'.  This  agreement  with 
the  results  obtained  from  the  northern  stars  is  extremely  sat- 
isfactory. 

If,  then,  the  progressive  motion  of  our  solar  system  may 
be  considered  as  determined  within  moderate  limits,  the 

*  In  a  letter  addressed  to  me.  See  Sebum.,  Astr.  Nachr.,  No.  622, 
6.  348. 

t  Galloway,  on  the  Motion  of  the  Solar  System,  in  the  Phdot.  Trant- 
act.  for  1847,  p.  98. 


MOTION  OF  THE  STARS.  197 

question  naturally  arises,  Is  the  world  of  the  fixed  stars  com- 
oosed  merely  of  a  number  of  neighboring  partial  systems  di- 
vided into  groups,  or  must  we  assume  the  existence  of  a  uni- 
versal relation,  a  rotation  of  all  self-luminous  celestial  bodies 
(suns)  around  one  common  center  of  gravity  which  is  either 
filed  u-ith  matter  or  void  ?  We  here,  however,  enter  the 
domain  of  mere  conjecture,  to  which,  indeed,  it  is  not  im- 
possible to  give  a  scientific  form,  but  which,  owing  to  the 
incompleteness  of  the  materials  of  observation  and  analogy 
which  are  at  present  before  us,  can  by  no  means  lead  to  the 
degree  of  evidence  attained  by  the  other  parts  of  astronomy 
The  fact  that  we  are  ignorant  of  the  proper  motion  of  an  in- 
finite number  of  very  small  stars  from  the  tenth  to  the  four- 
teenth magnitude,  which  appear  to  be  scattered  among  the 
brighter  ones,  especially  in  the  important  part  of  the  starry 
stratum  to  which  we  belong,  the  annuli  of  the  Milky  Way, 
is  extremely  prejudicial  to  the  profound  mathematical  treat- 
ment of  problems  so  difficult  of  solution.  The  contempla- 
tion of  our  own  planetary  sphere,  whence  we  ascend,  from 
the  small  partial  systems  of  the  moons  of  Jupiter,  Saturn, 
and  Uranus,  to  the  higher  and  general  solar  system,  has 
naturally  led  to  the  belief  that  the  fixed  stars  might  in  a 
similar  manner  be  divided  into  several  individual  groups, 
and  separated  by  immense  intervals  of  space,  which  again 
(in  a  higher  relation  of  these  systems  one  to  another)  may 
be  subject  to  the  overwhelming  attractive  force  of  a  great 
central  body  (one  sole  sun  of  the  whole  universe).*  The  in- 
ference here  advanced,  and  founded  on  the  analogy  of  our 
own  solar  system,  is,  however,  refuted  by  the  facts  hitherto 
observed.  In  the  multiple  stars,  two  or  more  self-luminous 
stars  (suns)  revolve,  not  round  one  another,  but  round  an 
external  and  distant  center  of  gravity.  No  doubt  something 
similar  takes  place  in  our  own  planetary  system,  inasmuch 
as  the  planets  do  not  properly  move  round  the  center  of  the 
solar  body,  but  around  the  common  center  of  gravity  of  all 
the  masses  in  the  system.  But  this  common  center  of  grav- 
ity falls,  according  to  the  relative  positions  of  the  great  plan- 
ets Jupiter  and  Saturn,  sometimes  within  the  circumference 
of  the  sun's  body,  but  oftener  out  of  it.f  The  center  of 
gravity,  which  in  the  case  of  the  double  stars  is  a  void  is 

*  Toe  value  or  worthlessness  of  such  views  has  been  discussed  by 
Argelanderin  his  essay, "  Ueber  die  eigene  Bewegung  des  Sonnensysteott 
kergelettet  avs  der  eigenen  Bewegwng  der  Sterne,  1837,  s.  39. 

t  See  Cosmot,  vol.  i.,  p.  145.     (Madler,  Attr.,  p.  400.) 


accordingly,  in  the  solar  system,  at  one  time  void,  at  another 
occupied  by  matter.  All  that  has  been  advanced  with  re- 
gard to  the  existence  of  a  dark  central  body  in  the  center 
of  gravity  of  double  stars,  or  at  least  of  one  originally  dark, 
but  faintly  illuminated  by  the  borrowed  light  of  the  planets 
which  revolve  round  it,  belongs  to  the  ever-enlarging  realm 
of  mythical  hypotheses. 

It  is  a  more  important  consideration,  and  one  more  de- 
serving of  thorough  investigation,  that,  on  the  supposition  of 
a  revolving  movement,  not  only  of  the  whole  of  our  planet- 
ary system  which  changes  its  place,  but  also  for  the  proper 
motion  of  the  fixed  ^stars  at  their  various  distances,  the  cen- 
ter of  this  revolving  motion  must  be  90°  distant*  from  the 
point  toward  which  our  solar  system  is  moving.  In  this  con- 
nection of  ideas,  the  position  of  stars  possessing  a  great  or 
very  small  proper  motion  becomes  of  considerable  moment. 
Argelander  has  examined,  with  his  usual  caution  and  acute- 
ness,  the  degree  of  probability  with  which  we  may  seek  for 
a  general  center  of  attraction  for  our  starry  stratum  in  the 
constellation  of  Perseus. t  Madler,  rejecting  the  hypothesis 
of  the  existence  of  a  central  body  preponderating  in  mass, 
as  the  universal  center  of  gravity,  seeks  the  center  of  grav- 
ity in  the  Pleiades,  in  the  very  center  of  this  group,  in  or 
nearf  to  the  bright  star  TJ  Tauri  (Alcyone).  The  present  is 

*  Argelander,  ibid.,  p.  42 ;  Madler,  CentraJsonne,  s.  9,  and  Astr.,  s. 
403. 

t  Argelauder,  ibid.,  p.  43  ;  and  in  Sebum.,  Astr.  Nachr.,  No.  566. 
Guided  by  no  numerical  investigations,  but  following  the  suggestions  of 
fancy,  Kant  long  ago  fixed  upon  Sirius,  and  Lambert  upon  the  nebula 
in  the  belt  of  Orion,  as  the  central  body  of  our  starry  stratum.  (Struve, 
Astr.  Stell.,  p.  17,  No.  19.) 

t  Madler,  Astr.,  s.  380,  400,  407,  and  414 ;  in  his  Centraltonne,  1846, 
p.  44-47  ;  in  Untersiickungen  uber  die  Fixstern-Systeme,  th.  ii.,  s.  183- 
185.  Alcyone  is  in  R.  A.  54°  30',  Decl.  23°  36',  for  the  year  1840.  If 
Alcyone's  parallax  were  really  0"-0065,  its  distance  would  be  equal  to 
3H  million  semi-diameters  of  the  earth's  orbit,  and  thus  it  would  be 
fifty  times  further  distant  from  us  than  the  distance  of  the  double  star 
61  Cygni,  according  to  Bessel's  earliest  calculation.  The  light  which 
comes  to  the  earth  from  the  sun  in  8'  18"-2,  would  in  that  case  take  500 
years  to  pass  from  Alcyone  to  the  earth.  The  fancy  of  the  Greeks  de- 
lighted itself  in  wild  visions  of  the  height  of  falls.  In  Hesiod's  Theo- 
gonia,  v.  722-725,  it  is  said,  speaking  of  the  fall  of  the  Titans  into  Tar- 
tarus:  "  If  a  brazen  anvil  were  to  fall  from  heaven  nine  days  and  nine 
nights  long,  it  would  reach  the  earth  on  the  tenth."  This  descent  of 
the  anvil  in  777,600  seconds  of  time  gives  an  equivalent  in  distance  of 
309,424  geographical  miles  (allowance  being  made,  according  to  Galle's 
calculation,  for  the  considerable  diminution  in  the  force  of  attraction  at 
planetary  distances),  therefore  1  i  times  the  distance  of  the  moon  from 


DOUBLE    STARS.  199 

not  the  place  to  discuss  the  probability  or  improbability*  of 
such  an  hypothesis.  Praise  is,  however,  due  to  the  eminent- 
ly active  director  of  the  Observatory  at  Dorpat  for  having, 
by  his  diligent  labors,  determined  the  positions  and  proper 
motions  of  more  than  800  stars,  and  at  the  same  time  ex- 
cited investigations  which,  if  they  do  not  lead  to  the  satis- 
factory solution  of  the  great  problem  itself,  are  nevertheless 
calculated  to  throw  light  on  kindred  questions  of  physical 
astronomy. 


VI. 

MULTIPLE  OR  DOUBLE  STARS.— THEIR  NUMBERS  AND  RECIPROCAL 
DISTANCES.— PERIOD  OF  REVOLUTION  OF  TWO  SUNS  ROUND  A  COM- 
MON CENTER  OF  GRAVITY. 

WHEN,  in  contemplating  the  systems  of  the  fixed  stars,  we 
descend  from  hypothetical,  higher,  and  more  general  consid- 
erations to  those  of  a  special  and  restricted  nature,  we  enter 
a  domain  more  clearly  determined,  and  better  calculated  for 
direct  observation.  Among  the  multiple  stars,  to  which  be- 
long the  binary  or  double  stars,  several  self-luminous  cosmic- 
al  bodies  (suns)  are  connected  by  mutual  attraction,  which 
necessarily  gives  rise  to  motions  in  closed  curved  lines.  Be- 
fore actual  observation  had  established  the  fact  of  the  revo- 
lution of  the  double  stars.t  such  movements  in  closed  curves 
were  only  known  to  exist  in  our  own  planetary  solar  system. 
On  this  apparent  analogy  inferences  were  hastily  drawn, 
which  for  a  long  time  gave  rise  to  many  errors.  As  the 
term  "  double  stars"  was  indiscriminately  applied  to  every 

the  earth.  But,  according  to  the  Iliad,  i.,  v.  592,  Hephaestus  fell  down 
to  Lemnos  in  one  day,  "when  but  a  little  breath  was  still  in  him." 
The  length  of  the  chain  hanging  down  from  Olympus  to  the  earth,  by 
which  all  the  gods  were  challenged  to  try  and  pull  down  Jupiter  (Il- 
iad, viii.,  v.  18),  is  not  given.  The  image  is  not  intended  to  convey  an 
idea  of  the  height  of  heaven,  but  of  Jupiter's  strength  and  omnipo- 
tence. 

*  Compare  the  doubts  of  Peters,  in  Schum.,  Astr.  Nachr.,  1849,  s. 
661,  and  Sir  John  Herschel,  in  the  Outl.  of  Astr.,  p.  589  :  "  In  the  pres- 
ent defective  state  of  our  knowledge  respecting  the  proper  motion  of 
the  smaller  stars,  we  can  not  but  regard  all  attempts  of  the  kind  as  to 
a  certain  extent  premature,  though  by  no  means  to  be  discouraged  as 
forerunners  of  something  more  decisive." 

t  Compare  Cosmos,  vol.  i.,  p.  146-149.  (Struve,  Ueber  Dopplesternc 
*ach  Dorpater  Micnmeter-Messungen  von  1824  bis  1837,  s.  11.) 


200  COSMOS. 

pair  of  stars,  the  close  proximity  of  which  precluded  their 
separation  by  the  naked  eye  (as  in  the  case  of  Castor,  a 
Lyrse,  (3  Orionis,  and  a  Centauri),  this  designation  naturally 
comprised  two  classes  of  multiple  stars  :  firstly,  those  which, 
from  their  incidental  position  in  reference  to  the  observer, 
appear  in  close  proximity,  though  in  reality  widely  distant 
and  belonging  to  totally  different  strata  ;  and,  secondly,  those 
which,  from  their  actual  proximity,  are  mutually  dependent 
upon  each  other  in  mutual  attraction  and  reciprocal  action, 
and  thus  constitute  a  particular,  isolated,  sidereal  system. 
The  former  have  long  been  called  optically,  the  latter  phys- 
ically, double  stars.  By  reason  of  their  great  distance,  and 
the  slowness  of  their  elliptical  motion,  many  of  the  latter  are 
frequently  confounded  with  the  former.  As  an  illustration 
of  this  fact,  Alcor  (a  star  which  had  engaged  the  attention  of 
many  of  the  Arabian  astronomers,  because,  when  the  air  is 
very  clear,  and  the  organs  of  vision  peculiarly  sharp,  this  small 
star  is  visible  to  the  naked  eye  together  with  £  in  the  tail  of 
Ursa  Major)  forms,  in  the  fullest  sense  of  the  term,  one  of 
these  optical  combinations,  without  any  closer  physical  con- 
nection.* In  sections  II.  and  III.  I  have  already  treated  of 
the  difficulty  of  separating  by  the  naked  eye  adjacent  stars, 
with  the  very  unequal  intensity  of  light,  of  the  influence  of 
the  higher  brilliancy  and  the  star's  tails,  as  well  as  of  the 
organic  defects  which  produce  indistinct  vision. 

Galileo,  without  making  the  double  stars  an  especial  ob- 
ject of  his  telescopic  observations  (to  which  his  low  magni- 
fying powers  would  have  proved  a  serious  obstacle),  men- 
tions (in  a  famous  passage  of  the  Giornata  terza  of  his  Dis- 
courses, which  has  already  been  pointed  out  by  Arago)  the 
use  which  astronomers  might  make  of  optically  double  stars 
(quando  si  trovasse  nel  telescopic  qualche  picciolissima  stella 
vicinissima  ad  alcuna  delle  maggiori)  for  determining  the 
parallax  of  the  fixed  stars,  t  As  late  as  the  middle  of  the 
last  century,  scarcely  twenty  double  stars  were  set  down  in 
the  stellar  catalogues,  if  we  exclude  all  those  at  a  greater 

*  Vide  tupra.  As  a  remarkable  instance  of  acuteness  of  vision,  we 
may  further  mention  that  MSstlin,  Kepler's  teacher,  discovered  with  the 
naked  eye  fourteen,  and  some  of  the  ancients  nine,  of  the  stars  in  the 
Pleiades.  (Madler,  Untersuch.  fiber  die  Fixslern-Systeme,  th.  ii.,  s.  36.) 

t  Vide  supra.  Dr.  Gregory,  of  Edinburgh,  also,  in  1675  (consequent- 
ly thirty-three  years  after  Galileo's  decease),  recommended  the  samo 
parallactic  method.  See  Thomas  Birch,  Hist,  of  the  Royal  Soe.,  vol. 
iii.,  1757,  p.  225.  Bradley  (1748)  alludes  to  this  method  at  the  conclu- 
sion of  his  celebrated  treatise  on  Nutation. 


DOUBLE  STARS.  201 

distance  from  each  other  than  32"  ;  at  present,  a  hundred 
yeais  later  (thanks  chiefly  to  the  great  labors  of  Sir  Will- 
iam Herschel,  Sir  John  Herschel,  and  Struve),  about  60UO 
have  been  discovered  in  the  two  hemispheres.  To  the  ear- 
liest described  double  stars*  belong  £  Ursae  maj.  (7th  Sep- 
tember, 1700,  by  Gottfried  Kirch),  a  Centauri  (1709,  by  Feu- 
illee),  y  Virginis  (1718),  a  Geminorum  (1719),  61  Cygni 
(1753)  (which,  with  the  two  preceding,  was  observed  by 
Bradley,  both  in  relation  to  distance  and  angle  of  direction), 
p  Ophiuclii  and  £  Cancri.  The  number  of  the  double  stars 
recorded  has  gradually  increased  from  the  time  of  Flamstead, 
who  employed  a  micrometer,  down  to  the  star-catalogue  of 
Tobias  Mayer,  which  appeared  in  1756.  Two  acutely  spec- 
ulative thinkers,  endowed  with  great  powers  of  combination, 
Lambert  (Photometria,  1760  ;  Kosmologische  Briefe  uber 
die  Einrichtung  des  Weltbaues,  1761)  and  John  Michell, 
1767,  though  they  did  not  themselves  observe  double  stars, 
were  the  first  to  diffuse  correct  views  upon  the  relations  of 
their  attraction  in  partial  binary  systems.  Lambert,  like 
Kepler,  hazarded  the  conjecture  that  the  remote  suns  (fixed 
stars)  are,  like  our  own  sun,  surrounded  with  dark  bodies, 
planets,  and  comets  ;  but  of  the  fixed  stars  proximate  to  each 
other,!  he  believed,  however  much,  on  the  other  hand,  he 
may  appear  inclined  to  admit  the  existence  of  dark  central 
bodies,  "  that  within  a  not  very  long  period  they  completed  a 
revolution  round  their  common  center  of  gravity."  Michell,$ 
who  was  not  acquainted  with  the  ideas  of  Kant  and  Lam- 
bert, was  the  first  who  applied  the  calculus  of  probabilities 
to  small  groups  of  stars,  which  he  did  with  great  ingenuity, 
especially  to  multiple  stars,  both  binary  and  quaternary.  He 
showed  that  it  was  500,000  chances  to  1  that  the  colloca- 
tion of  the  six  principal  stars  in  the  Pleiades  did  not  result 
from  accident,  but  that,  on  the  contrary,  they  owed  their 
grouping  to  some  internal  and  reciprocal  relation.  He  was 
so  thoroughly  convinced  of  the  existence  of  luminous  stars 
revolving  round  each  other,  that  he  ingeniously  proposed  to 
employ  these  partial  star-systems  to  the  solution  of  certain 
astronomical  problems.  $ 

*  Miicller,  Astr.,  s.  477.         t  Arago,  in  the  Annuairepour  1842,  p.  400. 

t  An  Inquiry  into  the  probable  parallax  and  magnitude  of  the  fixed 
stars,  from  the  quantity  of  light  which  they  afford  us,  and  the  particu- 
lar circumstances  of  their  situation,  by  the  Rev.  John  Michell;  in  the 
Pkilos.  Transact.,  vol.  Ivii.,  p.  234-261. 

$  John  Michell,  ibid.,  p.  238.  "  If  it  should  hereafter  be  found  that 
any  of  the  stars  have  others  revolving  about  them  (for  110  satellites  bv 


202  COSMOS. 

Christian  Mayer,  the  Manheim  astronomer,  has  the  great 
merit  of  having  first  (1778)  made  the  fixed  stars  a  special 
object  of  research,  by  the  sure  method  of  actual  observations. 
The  unfortunate  choice  of  the  term  satellites  of  the  fixed 
stars,  and  the  relations  which  he  supposed  to  exist  among 
the  stars  between  2°  30'  and  2°  55'  distant  from  Arcturus, 
exposed  him  to  bitter  attacks  from  his  cotemporaries,  and 
among  these  to  the  censure  of  the  eminent  mathematician, 
Nicolaus  Fuss.  That  dark  planetary  bodies  should  become 
visible  by  reflected  light,  at  such  an  immense  distance,  was 
certainly  improbable.  No  value  was  set  upon  the  results  of 
his  carefully-conducted  observations,  because  his  theory  of 
the  phenomena  was  rejected  ;  and  yet  Christian  Mayer,  in 
his  rejoinder  to  the  attack  of  Father  Maximilian  Hell,  Di- 
rector of  the  Imperial  Observatory  at  Vienna,  expressly  as- 
serts "  that  the  smaller  stars,  which  are  so  near  the  larger, 
are  either  illuminated,  naturally  dark  planets,  or  that  both 
of  these  cosmical  bodies — the  principal  star  and  its  compan- 
ion—  are  self-luminous  suns  revolving  round  each  other." 

a  borrowed  light  could  possibly  be  visible"),  we  should  then  have  the 
means  of  discovering "  Throughout  the  whole  discussion  he  de- 
nies that  one  of  the  two  revolving  stars  can  be  a  dark  planet  shining 
with  a  reflected  light,  because  both  of  them,  notwithstanding  their  dis- 
tance, are  visible  to  us.  Calling  the  larger  of  the  two  the  "  central 
star,"  he  compares  the  density  of  both  with  the  density  of  our  sun,  and 
merely  uses  the  word  "  satellite"  relatively  to  the  idea  of  revolution  or 
of  reciprocal  motion ;  he  speaks  of  the  "  greatest  apparent  elongation 
of  those  stars  that  revolve  about  others  as  satellites."  He  further  says, 
at  p.  243  and  249 :  "  We  may  conclude  with  the  highest  probability 
(the  odds  against  the  contrary  opinion  being  many  million  millions  to 
one)  that  stars  form  a  kind  of  system  by  mutual  gravitation.  It  is  high- 
ly probable  in  particular,  and  next  to  a  certainty  in  general,  that  such 
double  stars  as  appear  to  consist  of  two  or  more  stars  placed  near  to- 
gether are  under  the  influence  of  some  general  law,  such,  perhaps,  as 

gravity "     (Consult  also  Arago,  in  the  Annuaire  pour  1834,  p.  308, 

and  Ann.  1842,  p.  400.)  No  great  reliance  can  be  placed  on  the  indi- 
vidual numerical  results  of  the  calculus  of  probabilities  given  by  Michell, 
as  the  hypotheses  that  there  are  230  stars  ir  the  heavens  which,  in  in- 
tensity of  light,  are  equal  to  (3  Capricorn!,  KJid  1500  equal  to  the  six 
greater  stars  of  the  Pleiades,  are  manifestly  incorrect.  The  ingenious 
cosmological  treatise  of  John  Michell  ends  with  a  very  bold  attempt  to 
explain  the  scintillation  of  the  fixed  stars  by  a  kind  of  "  pulsation  in 
material  effluxes  of  light" — an  elucidation  not  more  happy  than  that 
which  Simon  Marius,  one  of  the  discoverers  of  Jupiter's  satellites  (see 
Cosmos,  vol.  ii.,  p.  320)  has  given  at  the  end  of  his  Mundus  Jovialis 
(1614).  But  Michell  has  the  merit  of  having  called  attention  to  the 
fact  (p.  263)  that  the  scintillation  of  stars  is  always  accompanied  by  a 
change  of  color.  "  Besides  their  brightness,  there  is  in  the  scintillation 
of  the  fixed  stars  a  change  of  color."  (  Vide  supra.) 


DOUBLE    STARS.  203 

The  importance  of  Christian  Mayer's  labors  has,  long  after 
his  death,  been  thankfully  and  publicly  acknowledged  by 
Struve  and  Madler.  In  his  two  treatises,  Vertheidigung 
neuer  Beobachtungen  von  Fixstern-trabanten  (1778),  and 
Dissertatio  de  novis  in  Ccdo  sidereo  Phcenomenis  (1779), 
eighty  double  stars  are  described  as  observed  by  him,  of 
which  sixty-seven  are  less  than  32"  distant  from  each  other. 
Most  of  these  were  first  discovered  by  Christian  Mayer  him- 
self, by  means  of  the  excellent  eight-feet  telescope  of  the  Man 
heim  Mural  Gluadrant ;  "  many  even  now  constitute  very 
difficult  objects  of  observation,  which  none  but  very  power- 
ful instruments  are  capable  of  representing,  such  as  p  and 
71  Herculis,  «  5  Lyrse,  and  GJ  Piscium."  Mayer,  it  is  true 
(as  was  the  practice  long  after  his  time),  only  measured  dis- 
tances in  right  ascension  and  declination  by  meridian  instru- 
ments, and  pointed  out,  from  his  own  observations,  as  well  as 
from  those  of  earlier  astronomers,  changes  of  position ;  but 
from  the  numerical  value  of  these,  he  omitted  to  deduct  what 
(in  particular  cases)  was  due  to  the  proper  motion  of  the  stars.* 
These  feeble  but  praiseworthy  beginnings  were  followed 
by  Sir  William  Herschel's  colossal  work  on  the  multiple  stars, 
which  comprises  a  period  of  more  than  twenty-five  years  ; 
for  although  Herschel's  first  catalogue  of  double  stars  was 
published  four  years  after  Christian  Mayer's  treatise  on  the 
same  subject,  yet  the  observations  of  the  former  go  back  as 
far  as  1779 — indeed,  even  to  1776,  if  we  take  into  consider- 
ation the  investigations  on  the  trapezium  in  the  great  nebula 
of  Orion.  Almost  all  we  at  present  know  of  the  manifold 
formation  of  the  double  stars  has  its  origin  in  Sir  William 
Herschel's  work.  In  the  catalogues  of  1782,  1783,  and 
1804,  he  has  not  only  set  down  and  determined  the  position 
and  distance  of  846  double  stars,!  for  the  most  part  first  dis- 
covered by  himself,  but,  what  is  far  more  important  than  any 
augmentation  of  number,  he  applied  his  sagacity  and  power 
of  observation  to  all  those  points  which  have  any  bearing  on 
their  orbits,  their  conjectured  periodic  times,  their  brightness, 
contrasts  of  colors,  and  classification  according  to  the  amount 

*  Struve,  in  the  Recueil  des  Actes  de  la  Stance  publique  de  VAcad. 
Imp.  des  Sciences  de  St.  Petersbourg,  le  29  Dec.,  1832,  p.  48-50.  Mad- 
ler, A*tr.,  s.  478. 

t  Philos.  Transact,  for  the  Year  1782,  p.  40-126;  for  1783,  p.  112- 
124 ;  for  1804,  p.  87.  Regarding  the  observations  on  which  Sir  Will- 
iam Herschel  founded  his  views  respecting  the  846  double  stars,  see 
Madler,  in  Schumacher's  Jahrbuchfur  1839,  s.  59,  and  his  Untertuchun- 
gen  itler  die  Fixstern-Systeme,  th.  i.,  18 17.  s.  7. 


204  COSMOS. 

of  their  mutual  distances.  Full  of  imagination,  yet  alwayg 
proceeding  with  great  caution,  it  was  not  till  the  year  1794, 
while  distinguishing  between  optically  and  physically  double 
Btars,  that  he  threw  out  his  preliminary  suggestions  as  to  the 
nature  of  the  relation  of  the  larger  star  to  its  smaller  com- 
panion. Nine  years  afterward,  he  first  explained  his  views 
of  the  whole  system  of  these  phenomena,  in  the  93d  volume 
of  the  Philosophical  Transactions.  The  idea  of  partial 
star-systems,  in  which  several  suns  revolve  round  a  common 
center  of  gravity,  was  then  firmly  established.  The  stupen- 
dous influence  of  attractive  forces,  which  in  our  solar  system 
extends  to  Neptune,  a  distance  30  times  that  of  the  earth 
(or  2488  millions  of  geographical  miles),  and  which  com- 
pelled the  great  comet  of  1680  to  return  in  its  orbit,  at  the 
distance  of  28  of  Neptune's  semi-diameters  (853  mean  dis- 
tances of  the  earth,  or  70,800  millions  of  geographical  miles), 
is  also  manifested  in  the  motion  of  the  double  star  61  Cygni, 
which,  with  a  parallax  of  0"-3744,  is  distant  from  the  sun 
18,240  semi-diameters  of  Neptune's  orbit  (i.  e.,  550,900 
earth's  mean  distances,  or  45,576,000  millions  of  geograph- 
ical miles).  But  although  Sir  William  Herschel  so  clearly 
discerned  the  causes  and  general  connection  of  the  phenome- 
na, still,  in  the  first  few  years  of  the  nineteenth  century,  the 
angles  of  position  derived  from  his  own  observations,  owing 
to  a  want  of  due  care  in  the  use  of  the  earlier  catalogues, 
were  confined  to  epochs  too  near  together  to  admit  of  perfect 
certainty  in  determining  the  several  numerical  relations  of 
the  periodic  times,  or  the  elements  of  their  orbits.  Sir  John 
Herschel  himself  alludes  to  the  doubts  regarding  the  accu- 
racy of  the  assigned  periods  of  revolution  of  a  Geminorum 
(334  years  instead  of  520,  according  to  Madler),*  of  y  Vir- 
ginis  (708  instead  of  169),  and  of  y  Leonis  (1424  of  Struve's 
great  catalogue),  a  splendid  golden  and  reddish-green  double 
star  (1200  years). 

After  William  Herschel,  the  elder  Struve  (from  1813  to 
1842)  and  Sir  John  Herschel  (from  1819  to  1838),  availing 
themselves  of  the  great  improvements  in  astronomical  in- 
struments, and  especially  in  micrometrical  applications,  have, 
with  praiseworthy  diligence,  laid  the  proper  and  special  foun- 

*  Madler,  ibid.,  th.  i.,  s.  255.  For  Castor  we  have  two  old  observa- 
tions of  Bradley,  1719  and  1759  (the  former  taken  in  conjunction  with 
Pond,  the  latter  with  Maskelyne),  and  two  of  the  elder  Herschel,  taken 
in  the  years  1779  and  1803.  For  the  period  of  revolution  of  y  Virginia, 
•ee  Madler,  Fixslern-Syst.,  th.  ii.,  s.  234-40,  1848. 


DOUBLE    STARS  205 

dation  of  this  important  branch  of  astronomy.  In  1820, 
Struve  published  his  first  Dorpat  Table  of  double  stars,  796 
in  number.  This  was  followed  in  1824  by  a  second,  con- 
taining 3112  double  stars,  down  to  the  ninth  magnitude,  in 
distances  under  32",  of  which  only  about  one  sixth  had  been 
before  observed.  To  accomplish  this  work,  nearly  120,000 
fixed  stars  were  examined  by  means  of  the  great  Fraun- 
hofer  refractor.  Struve's  third  table  of  multiple  stars  ap- 
peared in  the  year  1837,  and  forms  the  important  work  Stel- 
larum  compositarum  Mensurcs  Micrometrices.*  It  contains 
2787  double  stars,  several  imperfectly  observed  objects  being 
carefully  excluded. 

Sir  John  Herschel's  unwearied  diligence,  during  his  four 
years'  residence  in  Feldhausen,  at  the  Cape  of  Good  Hope, 
which,  by  contributing  to  an  accurate  topographical  knowl- 
edge of  the  southern  hemisphere,  constitutes  an  epoch  in 
astronomy,t  has  been  the  means  of  enriching  this  numbei 
by  the  addition  of  more  than  2100  double  stars  (which,  with 
few  exceptions,  had  never  before  been  observed).  All  these 
African  observations  were  taken  by  a  twenty-feet  reflecting 
telescope  ;  they  were  reduced  for  the  year  1830,  and  are 
included  in  the  six  catalogues  which  contain  3346  double 
stars,  and  were  transmitted  by  Sir  John  Herschel  to  the  As- 
tronomical Society  for  the  sixth  and  ninth  parts  of  their  val- 
uable Memoirs.^.  In  these  European  catalogues  are  laid 
down  the  380  double  stars  which  the  above  celebrated  as- 
tronomer had  observed  in  1825,  conjointly  with  Sir  James 
South. 

We  trace  in  this  historical  sketch  the  gradual  advance 
made  by  the  science  of  astronomy  toward  a  thorough  knowl- 
edge of  partial,  and  especially  of  binary  systems.  The  num- 
ber of  double  stars  (those  both  optically  and  physically  double) 
may  at  present  be  estimated  with  some  certainty  at  about 
6000,  if  we  include  in  our  calculation  those  observed  by  Bes- 
sel  with  the  excellent  Fraunhofer  heliometer,  by  Argelan- 
der§  at  Abo  (1827-1835),  by  Encke  and  G-alle  at  Berlin 

*  Struve,  Mensuree  Microm.,  p.  40  and  234-248.  On  the  whole, 
26414-146,  ».  e.,  2787  double  stars  have  been  observed.  (Madler,  in 
Sebum.,  Jakrb.,  1839,  s.  64.) 

t  Sir  John  Herschel,  Attron.  Observ.  at  the  Cape  of  Good  Hope,  p. 
16.5-303.  t  Ibid.,  p.  167  and  242. 

$  Argelander,  in  order  carefully  to  investigate  their  proper  motion, 
examined  a  great  number  of  fixed  stars.  See  his  essay,  entitled  "DLX. 
Stellarum  fixarum  positionet  media,  ineunte  anno  1830,  ex  observ.  Aboa 
habitit  (Heltingfortia,  1825)."  Madler  (Astr.,  a.  625)  estimates  the 


206  COSMOS. 

(1836  and  1839),  by  Preuss  and  Otto  Struve  in  Pulkowa 
(since  the  catalogue  of  1837),  by  Madler  in  Dorpat,  and  by 
Mitchell  in  Cincinnati  (Ohio),  with  a  seventeen-feet  Munich 
refractor.  How  many  of  these  6000  stars,  which  appear  to 
the  naked  eye  as  if  close  together,  may  stand  in  an  imme- 
diate relation  of  attraction  to  each  other,  forming  systems  of 
their  own,  and  revolving  in  closed  orbits — or,  in  other  words, 
how  many  are  so-called  physical  (revolving}  double  stars — 
is  an  important  problem,  and  difficult  of  solution.  More  re- 
volving companions  are  gradually  but  constantly  being  dis- 
covered. Extreme  slowness  of  motion,  or  the  direction  of  the 
plane  of  the  orbit  as  presented  to  the  eye,  being  such  as  to 
render  the  position  of  the  revolving  star  unfavorable  for  ob- 
servation, may  long  cause  us  to  class  physically  double  stars 
among  those  which  are  only  optically  so ;  that  is,  stars  of 
which  the  proximity  is  merely  apparent.  But  a  distinctly- 
ascertained  appreciable  motion  is  not  the  only  criterion.  The 
perfectly  uniform  motion  in  the  realms  of  space  (i.  e.,  a  com- 
mon progressive  movement,  like  that  of  our  solar  system,  in- 
cluding the  earth  and  moon,  Jupiter,  Saturn,  Uranus,  and 
Neptune,  with  their  satellites),  which  in  the  case  of  a  con- 
siderable number  of  multiple  stars  has  been  proved  by  Arge- 
lander  and  Bessel,  bears  evidence  that  the  principal  stars 
and  their  companions  stand  in  undoubted  relation  to  each 
other  in  separate  partial  systems.  Madler  has  made  the  in- 
teresting remark,  that  whereas,  previous  to  1836,  among 
2640  double  stars  that  had  been  catalogued,  there  were  only 
58  in  which  a  difference  of  position  had  been  observed  with 
certainty,  and  105  in  which  it  might  be  regarded  as  more 
or  less  probable ;  at  present,  the  proportion  of  physically 
double  stars  to  optically  double  stars  has  changed  so  greatly 
in  favor  of  the  former,  that  among  the  6000  double  stars, 
according  to  a  table  published  in  1849,  650  are  known  in 
which  a  change  of  relative  position  can  be  incontestably 
proved.*  The  earliest  comparison  gave  one  sixteenth,  the 

number  of  multiple  stars  in  the  northern  hemisphere,  discovered  at 
Pulkowa  since  1837,  at  not  less  than  600. 

*  The  number  of  fixed  stars  in  which  proper  motion  has  been  un- 
doubtedly discovered  (though  it  may  be  conjectured  in  the  case  of  all) 
is  slightly  greater  than  the  number  of  double  stars  in  which  change  of 
position  has  been  observed.  (Madler,  Astr.,  s.  394,  490,  and  520-540.) 
Results  obtained  by  the  application  of  the  Calculus  of  Probabilities,  ac- 
cording as  the  several  reciprocal  distances  of  the  double  stars  are  be- 
tween 0"  and  1",  2"  and  8  ,  or  16"  and  32",  are  given  by  Struve,  in  his 
Mens.  Microm.,  p.  xciv.  Distances  less  than  0"-8  have  been  taken,  and 


DOUBLE    STARS.  207 

most  recent  gives  one  ninth,  as  the  proportion  of  the  cosmic- 
al  bodies  which,  by  an  observed  motion  both  of  the  primary 
star  and  the  companion,  are  manifestly  proved  to  be  phys- 
ically double  stars. 

Very  little  has  as  yet  been  numerically  determined  re 
garding  the  relative  distribution  of  the  binary  star-systems 
throughout  space,  not  only  in  the  celestial  regions,  but  even 
on  the  apparent  vault  of  heaven.  In  the  northern  hemi- 
sphere, the  double  stars  most  frequently  occur  in  the  direc- 
tion of  certain  constellations  (Andromeda,  Bootes,  the  Great 
Bear,  the  Lynx,  and  Orion).  For  the  southern  hemisphere 
Sir  John  Herschel  has  obtained  the  unexpected  result,  "that 
in  the  extra-tropical  regions  of  this  hemisphere  the  number 
of  multiple  stars  is  far  smaller  than  that  in  the  correspond- 
ing portion  of  the  northern."  And  yet  these  beautiful  south- 
ern regions  have  been  explored,  under  the  most  favorable 
circumstances,  by  one  of  the  most  experienced  of  observers, 
with  a  brilliant  twenty-feet  reflecting  telescope,  which  sep- 
arated stars  of  the  eighth  magnitude  at  distances  even  of 
three  quarters  of  a  second.* 

The  frequent  occurrence  of  contrasted  colors  constitutes  an 
extremely  remarkable  peculiarity  of  multiple  stars.  Struve, 
in  his  great  workf  published  in  1837,  gave  the  following  re- 
sults with  regard  to  the  colors  presented  by  six  hundred  of 
the  brighter  double  stars.  In  375  of  these,  the  color  of  both 
principal  star  and  companion  was  the  same  and  equally  in- 
tense. In  101,  a  mere  difference  of  intensity  could  be  dis- 
cerned. The  stars  with  perfectly  different  colors  were  120 
in  number,  or  one  fifth  of  the  whole  ;  and  in  the  remaining 
four  fifths  the  principal  and  companion  stars  were  uniform  in 
color.  In  nearly  one  half  of  these  six  hundred,  the  princi- 
pal star  and  its  companion  were  white.  Among  those  of 
different  colors,  combinations  of  yellow  with  blue  (as  in  i 
Cancri),  and  of  orange  with  green  (as  in  the  ternary  star  y 
Andromedae),t  are  of  frequent  occurrence. 

Arago  was  the  first  to  call  attention  to  the  fact  that  the 
diversity  of  color  in  the  binary  systems  principally,  or  at  least, 
in  very  many  cases,  has  reference  to  the  complementary  col- 
experiments  with  very  complicated  systems  have  confirmed  the  astron- 
omer in  the  hope  that  these  estimates  are  mostly  correct  within  0"'l 
(Strnve,  iiber  Doppelsterne  nach  Dorpater  Beob.,  B.  29.) 

*  Sir  John  Herschel,  Observations  al  tht  Cape,  p.  166. 

t  Struve,  Mensurte  Microm.,  p.  Ixxvii.  to  Ixxxiv. 

t  Sir  John  Herschel,  Outlines  of  Aslr.,  p.  579. 


208  COSMOS. 

ors — the  subjective  colors,  which,  when  united,  form  white.* 
It  is  a  well  known  optical  phenomenon  that  a  faint  white 
light  appears  green  when  a  strong  red  light  is  brought  near 
it,  and  that  a  white  light  becomes  blue  when  the  stronger 
surrounding  light  is  yellowish.  Arago,  however,  with  his 
usual  caution,  has  reminded  us  of  the  fact  that  even  though 
the  green  or  blue  tint  of  the  companion  star  is  sometimes  the 
result  of  contrast,  still,  on  the  whole,  it  is  impossible  to  deny 
the  actual  existence  of  green  or  blue  stars. t  There  are  in- 

*  Two  glasses,  which  exhibit  complementary  colors  when  placed  one 
upon  the  other,  are  used  to  exhibit  white  images  of  the  sun.  During 
my  long  residence  at  the  Observatory  at  Paris,  my  friend  very  success- 
fully availed  himself  of  this  contrivance,  instead  of  using  shade  glasses 
to  observe  the  sun's  disk.  The  colors  to  be  chosen  are  red  and  green, 
yellow  and  blue,  or  green  and  violet.  "  Lorsqu'une  lumiere  forte  ue 
trouve  aupres  d'une  lumiere  faible,  la  derniere  prend  la  teinte  comple- 
mentaire  de  la  premiere.  C'est  la  le  contrast*;  mais  comme  le  rouge 
n'est  presque  jamais  pur,  on  peut  tout  aussi  bien  dire  que  le  rouge  est 
complementaire  du  bleu.  Les  couleurs  voisines  du  spectre  solaire  so 
substitueut."  "  When  a  strong  light  is  brought  into  contact  with  a 
feeble  one,  the  latter  assumes  the  complementary  color  of  the  former. 
This  is  the  effect  of  contrast ;  but  as  red  is  scarcely  ever  pure,  it  may 
as  correctly  be  said  that  red  is  the  complementary  of  blue :  the  colors 
nearest  to  the  solar  spectrum  reciprocally  change."  (Arago,  MS.  of 
1847.) 

t  Arago,  in  the  Connaisance  des  Temps  pour  Van  1 828,  p.  299-300 ; 
and  in  the  Annuaire  pour  1834,  p.  246-250;  pour  1842,  p.  347-350: 
"  Les  exceptions  que  je  cite,  prouvent  que  j'avais  bien  raison  en  1825 
de  n'introduire  la  notion  physique  du  contraste  dans  la  question  des  etoi- 
les  doubles  qu'avec  la  plus  grande  reserve.  Le  bleu  est  la  couleur  re- 
elle  de  certaines  etoiles.  II  resulte  des  observations  recueillies  jusqu'ici 
que  le  firmament  est  non  seulement  parseme  de  soleils  rouges  etjaunes, 
comme  le  savaient  les  auciens,  ma  isencore  de  soleils  Ileus  et  verts. 
C'est  au  terns  et  a  des  observations  futures  &  nous  apprendre  si  les  etoi- 
les vertes  et  bleues  ne  sont  pas  des  soleils  deja  en  voie  de  decroissance ; 
si  les  differentes  nuances  de  ces  astres  n'indiquent  pas  que  la  combustion 
s'y  ope  re  4  differens  degres ;  si  la  teinte,  avec  exces  de  rayons  les  plus 
refrangibles,  que  presente  souvent  la  petite  etoile,  ne  tiendrait  pas  a  la 
force  absorbante  d'une  atmosphere  que  developperait  Faction  de  *' etoile, 
ordinairement  beaucoup  plus  brillante,  qu'elle  accompagne."  "  The 
exceptions  I  have  named  proved  that  in  1825  I  was  quite  right  in  the 
cautious  reservations  with  which  I  introduced  the  physical  notion  of 
contrast  in  connection  with  double  stars.  Blue  is  the  real  color  of  cer 
tain  stars.  The  result  of  the  observations  hitherto  made  proves  that 
the  firmament  is  studded  not  only  with  red  and  yellow  suns  (as  was 
known  long  ago  to  the  ancients),  but  also  with  blue  and  green  suns. 
Time  and  future  observations  must  determine  whether  red  and  blue 
stars  are  not  suns,  the  brightness  of  which  is  already  on  the  wane; 
whether  the  varied  appearances  of  these  orbs  do  not  indicate  the  de- 
gree of  combustion  at  work  within  them ;  whether  the  color  and  the 
excess  of  the  most  refrangible  rays  often  presented  by  the  smaller  of 
two  stars  be  not  owing  to  the  absorbing  force  of  an  atmosphere  devel 


DOUBLE    STARS.  209 

stances  in  which  a  brilliant  white  star  (1527  Leonis,  1768 
Can.  ven.)  is  accompanied  by  a  small  blue  star ;  others,  where 
in  a  double  star  (8  Serp.)  both  the  principal  and  its  companion 
are  blue.*  In  order  to  determine  whether  the  contrast  of 
colors  is  merely  subjective,  he  proposes  (when  the  distance 
allows)  to  cover  the  principal  star  in  the  telescope  by  a  thread 
or  diaphragm.  Commonly  it  is  only  the  smaller  star  that 
is  blue :  this,  however,  is  not  the  case  in  the  double  star  23 
Orionis  (696  in  Struve's  Catalogue,  p.  Ixxx.),  where  the  prin- 
cipal star  is  bluish,  and  the  companion  pure  white.  If,  in 
the  multiple  stars,  the  differently  colored  suns  are  frequently 
surrounded  by  planets  invisible  to  us,  the  latter,  being  differ- 
ently illuminated,  must  have  their  white,  blue,  red,  and  green 
days.f 

As  the  periodical  variability^,  of  the  stars  is,  as  we  have 
already  pointed  out,  by  no  means  necessarily  connected  with 
their  red  or  reddish  color,  so  also  coloring  in  general,  or  a 
contrasting  difference  of  the  tones  of  color  between  the  prin- 
cipal star  and  its  companion,  is  far  from  being  peculiar  to 
the  multiple  stars.  Circumstances  which  we  find  to  be  fre- 
quent are  not,  on  that  account,  necessary  conditions  of  the 
phenomena,  whether  relating  to  a  periodical  change  of  light, 
or  to  the  revolution  in  partial  systems  round  a  common  cen- 
ter of  gravity.  A  careful  examination  of  the  bright  double 
stars  (and  color  can  be  determined  even  in  those  of  the  ninth 
magnitude)  teaches  that,  besides  white,  all  the  colors  of  the 
solar  spectrum  are  to  be  found  in  the  double  stars,  but  that 
the  principal  star,  whenever  it  is  not  white,  approximates  in 
general  to  the  red  extreme  (that  of  the  least  refrangible  rays), 
but  the  companion  to  the  violet  extreme  (the  limit  of  the 
most  refrangible  rays).  The  reddish  stars  are  twice  as  fre- 
quent as  the  blue  and  bluish  ;  the  white  are  about  21  times 
as  numerous  as  the  red  and  reddish.  It  is  moreover  remark- 
able that  a  great  difference  of  color  is  usually  associated  with 

oped  by  the  action  of  the  accompanying  star,  -which  is  generally  much 
the  more  brilliant  of  the  two."  (Arago,  in  the  Annuairepour  1834,  p. 
295-301.) 

*  Struve,  Ueber  Doppdtterne  nach  Dorpater  Beobachtungen,  1837,  a. 
33-36,  and  Mensurce  Microm.,  p.  Ixxxiii.,  enumerates  sixty-three  double 
Btarsin  which  both  the  principal  and  companion  are  blue  or  bluish,  and 
in  which,  therefore,  the  colcrs  can  not  be  the  effect  of  contrast.  When 
\ve  are  forced  to  compare  together  the  colors  of  double  stars,  as  report- 
ed by  several  astronomers,  it  is  particularly  striking  to  observe  how  fre- 
quently the  companion  of  a  red  or  orange-colored  star  is  reported  by 
some  observers  as  blue,  and  by  others  as  green. 

t  Arago,  Annuain  pour  1834,  p.  302.         t  Vide  tupra,  p.  130-136. 


210  COSMOS. 

a  corresponding  difference  in  brightness.  In  two  cases — in 
£  Bootis  and  y  Leonis — which,  from  their  great  brightness, 
can  easily  be  measured  by  powerful  telescopes,  even  in  the 
daytime,  the  former  consists  of  two  white  stars  of  the  third 
and  fourth  magnitudes,  and  the  latter  of  a  principal  star  of 
the  second,  and  of  a  companion  of  the  3 -5th  magnitude. 
This  is  usually  called  the  brightest  double  star  of  the  north- 
ern hemisphere,  whereas  a  Centauri*  and  a  Crucis,  in  the 
southern  hemisphere,  surpass  all  the  other  double  stars  in 
brilliancy.  As  in  £  Bootis,  so  also  in  a  Centauri  and  y  Leonis, 
we  observe  the  rare  combination  of  two  great  stars  with  only 
a  slightly  different  intensity  of  light. 

No  unanimity  of  opinion  yet  prevails  respecting  the  vari- 
able brightness  in  multiple  stars,  and  especially  in  that  of 
companions.  We  have  already t  several  times  made  mention 
of  the  somewhat  irregular  variability  of  luster  in  the  orange- 
colored  principal  star  in  a  Herculis.  Moreover,  the  fluctua- 
tion in  the  brightness  of  the  nearly  equal  yellowish  stars  (of 
the  third  magnitude)  constituting  the  double  star  y  Virginis 
and  Anon.  2718,  observed  by  Struve  (1831-1833),  probably 
indicates  a  very  slow  rotation  of  both  suns  upon  their  axes.J 
Whether  any  actual  change  of  color  has  ever  taken  place 
in  double  stars  (as,  for  instance,  in  y  Leonis  and  y  Delphini)  ; 
whether  their  white  light  becomes  colored,  and,  on  the  other 
hand,  whether  the  colored  light  of  the  isolated  Sirius  has  be- 
come white,  still  remain  undecided  questions. §  Where  the 
disputed  differences  refer  only  to  faint  tones  of  color,  we  should 
take  into  consideration  the  power  of  vision  of  the  observer, 
and,  if  refractors  have  not  been  employed,  the  frequently  red- 
dening influence  of  the  metallic  speculum. 

Among  the  multiple  systems  we  may  cite  as  ternaries,  £ 
Librae,  £  Cancri,  12  Lyncis,  11  Monoc.  ;  as  quaternaries, 
102  and  2681  of  Struve's  Catalogue,  a  Andromedae,  e  Lyrae  : 
in  6  Orionis,  the  famous  trapezium  of  the  greater  nebula  of 

*  "  This  superb  double  star  (a  Cent.)  is  beyond  all  comparison  the 
most  striking  object  of  the  kind  in  the  heavens,  and  consists  of  two  in- 
dividuals, both  of  a  high  ruddy  or  orange  color,  though  that  of  the 
smaller  is  of  a  somewhat  more  somber  and  brownish  cast."  (Sir  John 
Herschel,  Observations  at  the  Cape  of  Good  Hope,  p.  300.)  And,  ac- 
cording to  the  important  observations  taken  by  Captain  Jacob,  of  the 
Bombay  Engineers,  between  the  years  1846  and  1848,  the  principal  star 
is  estimated  of  the  first  magnitude,  and  the  satellite  from  the  2'5th  to 
the  third  magnitude.  (  Transact,  of  tht  Royal  Soc.  of  Edinb.,  vol.  X'vn 
1849,  p.  451.) 

t  Videtupra,  p.  165,  166,  and  note. 

t  Struve,  Ueber  Doppeltt.  nach  Dorp  Beob.,  s.  33.         $  Ibid.,  s.  36 


DOUBLE  STARS.  211 

Orion,  we  have  a  combination  of  six — probably  a  system  sub- 
ject to  peculiar  physical  attraction,  since  the  five  smaller 
stars  (6'3m. ;  7m.;  8m.;  ll'Sm. ;  and  12m.)  follow  the  prop- 
er motion  of  the  principal  star,  4-7m.  No  change  in  their 
relative  positions  has  yet  been  observed.*  In  the  ternary 
combinations  of  £  Librae  and  £  Cancri,  the  periodical  move- 
ment of  the  two  companions  has  been  recognized  with  great 
certainty.  The  latter  system  consists  of  three  stars  of  the 
third  magnitude,  differing  very  little  in  brightness,  and  the 
nearer  companion  appears  to  have  a  motion  ten  times  more 
rapid  than  the  remoter  one. 

Tho  number  of  the  double  stars,  the  elements  of  whose 
orbits  it  has  been  found  possible  to  determine,  is  at  present 
stated  at  from  fourteen  to  sixteen. t  Of  these,  £  Herculis 
has  twice  completed  its  orbit  since  the  epoch  of  its  first  dis- 
covery, and  during  this  period  has  twice  (1802  and  1831) 
presented  the  phenomenon  of  the  apparent  occultation  of  one 
fixed  star  by  another.  For  the  earliest  measurements  of 
the  orbits  of  double  stars,  we  are  indebted  to  the  industry  of 
Savary  (£  Ursae  Maj.),  Encke  (70  Ophiuchi),  and  Sir  John 
Herschel.  These  have  been  subsequently  followed  by  Bes- 
sel,  Struve,  Madler,  Hind,  Smyth,  and  Captain  Jacob.  Sa- 
vary's  and  Encke's  methods  require  four  complete  observa- 
tions, taken  at  sufficient  intervals  from  each  other.  The 
shortest  periods  of  revolution  are  thirty,  forty- two,  fifty-eight, 
and  seventy-seven  years  ;  consequently,  intermediate  be- 
tween the  periods  of  Saturn  and  Uranus ;  the  longest  that 
have  been  determined  with  any  degree  of  certainty  exceed 
five  hundred  years,  that  is  to  say,  are  nearly  equal  to  three 
times  the  period  of  Le  Verrier's  Neptune.  The  eccentricity 
of  the  elliptical  orbits  of  the  double  stars,  according  to  the 
investigations  hitherto  made,  is  extremely  considerable,  re- 
sembling that  of  comets,  increasing  from  0'62  (a  Coronae)  up 
to  0'95  (a  Centauri).  The  least  eccentric  interior  comet—- 
that of  Faye — has  an  eccentricity  of  0-55,  or  less  than  that 
of  the  orbits  of  the  two  double  stars  just  mentioned.  Ac- 
cording to  Midler's  and  Hind's  calculations,  i\  Coronas  and 
Castor  exhibit  much  less  eccentricity,  which  in  the  former  is 
0-29,  and  in  the  latter  0-22  or  0-24.  In  these  double  stars  the 
two  suns  describe  ellipses  which  come  very  near  to  those  of 

*  Madler,  Astr.,  s.  517.     Sir  John  Herschel,  Ovtl.,  p.  568. 

t  Compare  Madler,  Untertuch.  uber  die  Fixstcm-Systeme,  th.  i.,  s. 
225-273 ;  th.  ii.,  s.  235-240 ;  and  his  Astr.,  a.  541  Sir  John  HerscheL 
Outl.,  p.  573. 


212  COSMOS. 

two  of  the  smaller  principal  planets  in  our  solar  system,  the 
eccentricity  of  the  orhit  of  Pallas  being  0-24,  and  that  of 
Juno,  0-25. 

If,  with  Encke,  we  consider  one  of  the  two  stars  in  a  bi- 
nary system,  the  brighter,  to  be  at  rest,  and  on  this  supposi- 
tion refer  to  it  the  motion  of  the  companion,  then  it  follows 
from  the  observations  hitherto  made  that  the  companion  de- 
scribes round  the  principal  star  a  conic  section,  of  which  the 
latter  is  the  focus ;  namely,  an  ellipse  in  which  the  radius 
vector  of  the  revolving  cosmical  body  passes  over  equal  su- 
perficial areas  in  equal  times.  Accurate  measurements  of 
the  angles  of  position  and  of  distances,  adapted  to  the  determ- 
ination of  orbits,  have  already  shown,  in  a  considerable  num- 
ber of  double  stars,  that  the  companion  revolves  round  the 
principal  star  considered  as  stationary,  impelled  by  the  same 
gravitating  forces  which  prevail  in  our  own  solar  system. 
This  firm  conviction,  which  has  only  been  thoroughly  attain- 
ed within  the  last  quarter  of  a  century,  marks  a  great  epoch 
in  the  history  of  the  development  of  higher  cosmical  knowl- 
edge. Cosmical  bodies,  to  which  long  use  has  still  preserved 
the  name  of  fixed  stars,  although  they  are  neither  riveted 
to  the  vault  of  heaven  nor  motionless,  have  been  observed 
to  occult  each  other.  The  knowledge  of  the  existence  of 
partial  systems  of  independent  motion  tends  the  more  to  en- 
large our  view,  by  showing  that  these  movements  are  them- 
selves subordinate  to  more  general  movements  animating  th» 
regions  of  space. 


DOUBLE    STARS. 
ELEMENTS  OF  THE  ORBITS  OF  DOUBLE  STARS. 


213 


_t 

Semi-Major 
Axis. 

Eccentricity. 

Period  of 
Revolution 
in  yean. 

Calculator. 

(1)  f  UrsseMaj.... 

3"-857 

0-4164 

58-262 

Savary,    1830. 

3"-278 
2"-295 

0-3777 
04037 

60-720 
61-300 

John  Herschel. 
Tables  of  1849. 
Madler,     1847. 

(2)  pOphiuchi  

4"-328 

04300 

73-862 

Encke,     1832. 

(3)  fHerculis  
(4)  Castor 

1"-208 
8"-086 

04320 
0-7582 

3022 
252-66 

Madler,     1847 
John  Herschel 

5"-692 

0-2194 

519-77 

Tables  of  1849. 
Madler,     1847. 

6"-300 

0-2405 

632-27 

Hind,        1849. 

(5)  y  Virginia  

3"-580 
3"-863 

0-8795 
0-8806 

182-12 
169-44 

John  Herschel. 
Tables  of  1849. 
Madler,     1847. 

(6)  oCentauri  

15"-500 

09500 

7700 

Captain  Jacob, 
1848. 

INDEX  TO   VOL.  III. 


ACHROMATIC  telescopes,  63. 

Adalbert,  Prince,  of  Prussia,  his  observa- 
tions on  the  undulation  of  the  stars,  59. 

Alcor,  a  star  of  the  constellation  Ursa  Ma- 
jor, employed  by  the  Persians  as  a  test 
of  vision,  49,  50,  200. 

Alcyone,  one  of  the  Pleiades,  imagined 
the  center  of  gravity  of  the  solar  sys- 
tem by  Madler,  198. 

Alphonsine  Tables,  date  of  their  construc- 
tion, 151. 

Anaxagoras  of  Clazomense,  his  theory 
of  the  world-arranging  intelligence,  11 ; 
origin  of  the  modern  theories  of  rota- 
tory motion,  12. 

Andromeda's  girdle,  nebula  in,  142. 

Arago,  M.,  letters  and  communications  of, 
to  M.  Humboldt,  46,  49,  67,  68,  73,  96, 
207-209 ;  on  the  effect  of  telescopes  on 
the  visibility  of  the  stars,  69 ;  on  the 
velocity  of  light,  80, 84 ;  on  photometry, 
92,  90 ;  his  cyanometer,  97. 

Aratus,  a  fragment  of  the  work  of  Hip- 
parchas  preserved  in,  109. 

Archimedes,  his  "  Arenarius,"  30. 

Avcturus,  true  diameter  of,  89. 

Argulander,  his  view  of  the  number  of 
the  fixed  stars,  105,  106 ;  his  additions 
to  Bessel's  Catalogue,  115 ;  on  period- 
ically variable  stars,  166. 

ij  Argus,  changes  in  color  and  brilliancy 
of,  135,  178,  179. 

Aristotle,  his  distinct  apprehension  of  the 
unity  of  nature,  13-15;  his  defective 
solution  of  the  problem,  15;  doubts  the 
infinity  of  space,  29, 30 ;  his  idea  of  the 
generation  of  heat  by  the  movement  of 
the  spheres,  124. 

aosy,  the  domain  of  the  fixed  stars, 


Astronomy,  the  observation  of  groups  of 
fixed  stars,  the  first  step  in,  118 ;  very 
bright  single  stars,  the  first  named,  89. 

Atmosphere,  limits  of  the,  40,  41 ;  effects 
of  an  untransparent,  104. 

Augustine,  St.,  cosmical  views  of,  124. 

Autolycus  of  Pitane,  era  of,  89,  90. 

Auzout's  object-glasses,  62. 

Bacon,  Lord,  the  earliest  views  on  the  ve- 
locity of  light  found  in  his  "Novum 
Organum,"  79. 

Baily ,  Francis,  his  revision  of  De  Lalande's 
Catalogue,  115. 

Bayer's  lettering  of  the  stars  of  any  con- 
stellation not  an  evidence  of  their  rel- 
ative brightness,  98. 

Berard,  Captain,  on  the  change  of  color 
of  the  star  y  Crucis,  135. 


Berlin  Academy,  star  maps  of  the,  11B. 

Bessel,  on  repulsive  force,  34,  35 ;  his  star 
maps  have  been  the  principal  means  of 
the  recognition  of  seven  new  planets, 
116 ;  calculation  of  the  orbits  of  double 
stars  by,  211. 

Binary  stars,  199. 

Blue  stars,  136 ;  less  frequent  than  red,  209. 

Blue  and  green  suns,  the  probable  cause 
of  their  color,  208. 

Bond,  of  the  Cambridge  Observatory, 
United  States,  his  resolution  of  the  neb- 
ula in  Andromeda's  girdle  into  small 
stars,  142. 

Brewster,  Sir  David,  on  the  dark  lines  of 
the  prismatic  spectra,  44. 

British  Association,  their  edition  of  La- 
lande's Catalogue,  115. 

Bruno,  Giordano,  his  cosmical  views,  17 ; 
his  martyrdom,  17. 

Busch,  Dr.,  his  estimate  of  the  velocity  of 
light  incorrect,  82. 

Catalogues,  astronomical,  their  great  im- 
portance, 113,  114  ;  future  discoveries 
of  planetary  bodies  mainly  dependent 
on  their  completeness,  114  ;  list  of,  114, 
115 ;  Halley's,  Flamstead's,  and  others, 
114 ;  Lalande's,  Harding's,  Bessel's,  115 

Catasterisma  of  Eratosthenes,  89,  90. 

a  Centauri,  Piazzi  Smyth  on,  146, 147, 185; 
the  nearest  of  the  fixed  stars  that  have 
yet  been  measured,  191,  192. 

Central  body  for  the  whole  sidereal  heav- 
ens, existence  of,  doubtful,  197. 

Chinese  record  of  extraordinary  stars  (of 
Ma-tuan-lin),  109, 155-159;  deserving  of 
confidence,  162. 

Clusters  of  stars,  or  stellar  swarms,  140 ; 
list  of  the  principal,  141-143. 

Coal-sacks,  a  portion  of  the  Milky  Way  in 
the  southern  hemisphere  so  called,  137. 

Colored  rings  afford  a  direct  measure  of 
the  intensity  of  light,  96. 

Colored  stars,  130;  evidence  of  change 
of  color  in  some,  131,  132;  Sir  John 
Herschel's  hypothesis,  131 ;  difference 
of  color  usually  accompanied  by  differ 
ence  of  brightness,  209. 

Comets,  information  regarding  celestial 
space,  derived  from  observation  on,  31, 
39 ;  number  of  visible  ones,  151. 

Concentric  rings  of  stars,  a  view  favored 
by  recent  observation,  149. 

Constellations,  arrangement  of  stars  into, 
very  gradual,  119. 

Contrasted  colors  of  double  stars,  207. 

Cosmical  contemplation,  extension  of,  la 
the  Middle  Ages,  16. 


Cosmical  vapor,  question  as  to  condensa- 
tion of,  37 ;  Tycho  Brahe's  and  Sir  Will- 
iam  Herschel's  theories,  154. 

"  Cosmos,"  a  pseudo-Aristotelian  work, 
16. 

Crystal  vault  of  heaven,  date  of  the  desig- 
nation, 133 ;  its  signification  according 
to  Empedocles,  123 ;  the  idea  favored 
by  the  Fathers  of  the  Church,  125. 

Cyanometer,  Arago's,  97. 

Dark  cosmical  bodies,  question  of,  164, 
187. 

Dolambrc  on  the  velocity  of  light,  82. 

Descartes,  his  cosmical  views,  19, 20 ;  sup- 
presses his  work  from  deference  to  the 
Inquisition,  20. 

Dioptric  tubes,  the  precursors  of  the  tele- 
scope, 43. 

Direct  and  reflected  light,  45. 

Distribution  of  the  fixed  stars,  according 
to  right  ascension,  140. 

Dorpat  Table  (Struve's)  of  multiple  stars, 
205. 

Double  stars,  the  name  too  indiscrimin- 
ately applied,  199, 200 ;  distribution  into 
optical  and  physical.  200 ;  pointed  out 
by  Galileo  as  useful  in  determining  the 
parallax,  200 ;  vast  increase  in  their  ob- 
served number,  201, 205;  those  earliest 
described,  201;  number  in  which  a 
change  of  position  has  been  proved, 
206 ;  greater  number  of  double  stars  in 
the  northern  than  in  the  southern  hem- 
isphere, 207  ;  occurrence  of  contrasted 
colors,  207 ;  calculation  of  their  orbits, 
211 ;  table  of  the  elements,  213. 

Earth-animal,  Kepler  and  Fludd's  fancies 

regarding  the,  19. 
Edda-Songs,  allusion  to,  8. 
Egypt,  zodiacal  constellations   of,  their 

date,  121. 
Egyptian  calendar,  period  of  the  complete 

arrangement  of  the,  133. 
Ehrenberg  on  the  incalculable  number 

of  animal  organisms,  30. 
Electrical  light,  velocity  of  transmission 

of,  86. 
Electricity,  transmission  of,  through  the 

Elements,  Indian  origin  of  the  hypothesis 
of  four  or  five,  11. 

Emanations  from  the  head  of  some  com- 
ets, 39. 

Encke,  his  accurate  calculation  of  the 
equivalent  of  an  equatorial  degree,  81 ; 
on  the  star-maps  of  the  Berlin  Academy, 
116 ;  an  early  calculator  of  the  orbits 
of  double  stars,  2C  \ ;  his  theory  of  their 
motion,  212. 

Encke's  comet,  considerations  on  space, 
derived  from  periods  of  revolution  of, 
27;  a  resisting  medium  proved  from 
observation  on,  39. 

Ether,  different  meanings  of,  in  the  East 
and  the  West,  31,  32. 

Ether  (Ak£ so,  in  Sanscrit),  one  of  the  In- 
dian five  elements,  31. 

Ether,  the,  fiery,  35. 


Euler's  comparative  estimate  of  the  light 
f  the  sun  and  moon,  95. 

Fixed  stars,  the  term  erroneous,  27, 122 ; 
scintillation  of  the,  73  ;  variations  in  its 
intensity,  76 ;  our  sun  one  of  the  fainter 
fixed  stars,  95;  photometric  arrange- 
ment of,  99 ;  their  number,  105 ;  num- 
ber visible  at  Berlin  with  the  naked  eye, 
107;  at  Alexandria,  107;  Struve  and 
Herschel's  estimates,  116;  grouping  of 
the,  117 ;  distribution  of  the,  140 ;  prop- 
er motion  of  the,  182 ;  parallax,  188 ; 
number  of,  in  which  proper  motion  has 
been  discovered,  greater  than  of  those 
in  which  change  of  position  has  been 
observed,  206,  207. 

Fizeau,  M.,  his  experiments  on  the  veloc- 


ity of  light,  80,  83. 
Formula  for 


computing  variation  of  light 
of  a  star,  by  Argelander,  : 


Galactic  circle,  average  number  of  stars 
in,  and  beyond  the,  139. 

Galileo  indicates  the  means  of  discover- 
ing the  parallax,  188. 

Galle,  Dr.,  on  Jupiter's  satellites,  50 ;  on 
the  photometric  arrangement  of  the 
fixed  stars,  99. 

Garnet  star,  the,  a  star  in  Cepheus,  so 
called  by  William  Hcrschel,  1G6. 

Gascoigne  applies  micrometer  threads  to 
the  telescope,  42. 

Gauging  the  heavens,  by  Sir  William  Her- 
schel,  138,  139 ;  length  of  time  neces- 
sary to  complete  the  process,  139. 

Gauss,  on  the  point  of  translation  in  space 
of  the  whole  solar  system,  196. 

Gilliss,  Lieutenant,  on  the  change  of  color 
of  the  star  ij  Argus,  135. 

Gravitation,  not  an  essential  property  of 
bodies,  but  the  result  of  some  higher 
and  still  unknown  power,  22,  23. 

Greek  sphere,  date  of  the,  119,  121. 

Green  and  blue  suns,  208. 

Groups  of  fixed  stars,  recognized  even 
by  the  rudest  nations,  117 ;  usually  the 
same  groups,  as  the  Pleiades,  the  Great 
Bear,  the  Southern  Cross,  &c.,  117, 118. 

Halley  asserted  the  motion  of  Sinus  and 
other  fixed  stars,  26,  27. 

Hassenfratz,  his  description  of  the  rays 
of  stars  as  caustics  on  the  crystalline 
lens,  52,  127. 

Heat,  radiating,  35. 

Hepidannus,  monk  of  Saint  Gall,  a  new 
star  recorded  by,  157,  162. 

Herschel,  Sir  William,  on  the  vivifying 
action  of  the  sun's  rays,  34 ;  his  estimate 
of  the  number  of  the  fixed  stars,  116, 
117 ;  his  "  gauging  the  heavens,"  and  its 
result,  138,  139. 

Herschel,  Sir  John,  on  the  transmission 
of  light,  30 ;  on  the  influence  of  the  sun'g 
rays,  34 ;  compares  the  sun  to  a  per- 
petual northern  light,  34 ;  on  the  at- 
mosphere, 37 ;  on  the  blackness  of  the 
ground  of  the.  heavens,  39 ;  on  stars 
seen  in  daylight^  57;  on  photometry. 


217 


93  ;   photometric  arrangement  of  the 
fixed  stars,  99  ;  on  the  number  of  stars 

Lassell's  telescope,  discoveries  made  by 
means  of,  65. 

actually  registered.  106  ;  on  the  cause 
of  the  red  color  of  Sirius,  131,  132  ;  on 

Lepsius,  on  the  Egyptian  name  (Sothis) 
of  Sinus,  134. 

fhe  Milky  Way,  145;  on  the  sun's  place, 
150;  on  the  determined  periods  of  vari- 

Leslie's photometer,  defects  of,  96. 
Libra,  the  constellation,  date  of  its  intro- 

able stars,  166;  number  of  double  stars 

duction  into  the  Greek  sphere,  120. 

the  elements  of  whose  orbits  have  been 

Light,  always  refracted,  44  ;    prismatic 

determined,  211. 

spectra  differ  in  number  of  dark  lines 

Hieroglyphical  signification  of  a  star,  ac- 
cording to  Horapollo,  128. 

according  to  their  source,  44,  45  ;  polar- 
ization of,  45  ;  velocity  of,  79  ;  ratio  of 

Hind's  discovery  of  a  new  reddish-yellow 

solar,  lunar,  and  stellar,  95  ;  variation 

star  of  the  fifth  magnitude,  in  Ophiu- 

of,  in  stars  of  ascertained  and  unascer- 

magnitude, 160  ;  calculation  of  the  or- 

tained periodicity,  168,  177. 
Light  of  the  sun  and  moon,  Euler's  and 

bits  of  double  stars  by,  211. 
Hipparchus.  on  the  number  of  the  Plei- 

Michelo's estimates  of  the  comparative, 
95. 

ades,  48  ;    his   catalogue   contains  the 

Limited  transparency  of  the  celestial  re- 

earliest determination  of  the  classes  of 

gions.  38. 

magnitude  of  the  stars,  90  ;  a  fragment 
of  his  work  preserved  to  us  in  Aratus, 

IftO 

Macrobius,  "  Sphsera  aplanes"  of,  27. 
Madler,  on  Jupiter's  satellites.  52  ;  on  the 

ioy. 

Holtzmann,  on  the  Indian  zodiacs,  121. 
Homer,  not  an  authority  on  the  state  of 
Greek  astronomy  in  his  day,  119,  123. 
Humboldt,    Alexander    von,   works   of, 
quoted  in  various  notes: 
Ansichten  der  Natur,  79. 
Asie  Centrale,  111,  112. 
Essai  sur  la  Geogr.  des  Plantes,  58. 
Examen  Critique  de  1'Histoire  de  la 

determined  periods  of  variable  stars, 
166;  on  future  polar  stars,  181  ;  on  non- 
luminous  stars,  187  ;  on  the  center  of 
gravity  of  the  solar  system,  198. 
Magellanic  clouds,  known  to  the  Arabs,  91. 
Magnitude  of  the  stars,  classes  of,  90,  91. 
Mafus,  his  discoveries  regarding  light,  45. 
'•  Mappa  ccelestis"  of  Schwinck,  140. 
Ma-tuan-lin,  a  Chinese  astronomical  rec- 
ord of  109 

G6ographie,  49,  112,  137. 
Lettre  a  M.  Schumacher,  93. 
Recueil      d'Observations      Astrono- 
miques,  43.  47,  93. 
Relation  Historique  du  Voyage  aux 
Regions  Equinoxiales,  56,  58.  79,  93. 
Vue  des  Cordilleres  et  Monumens 
des  Peuples  Indigenes  de  1'Amer- 

Mayer,  Christian,  the  first  special  observer 
of  the  fixed  stars,  202. 
Melville  Island,  temperature  of,  36. 
Michell,  John,  95  ;  applies  the  calculus  of 
probabilities  to  small  groups  of  stars, 
201  ;  little  reliance  to  be  placed  in  its 
individual  numerical  result?,  202. 
Michelo's   comparative   estimate   of  the 

ique,  121,  136. 
Humboldt,  Wiihelm  von,  quoted,  25. 
Huygens,  Christian,  his  ambitious  but  un- 
satisfactory Cosmotheoros,  20;  exam- 
ined the  Milky  Way,  144. 

light  of  the  sun  and  moon,  95. 
Milky  Way,  average  number  of  stars  in, 
and  beyond  the,  according  to  Struve, 
139  ;  intensity  of  its  light  in  the  vicinity 
of  the  Southern  Cross,  147  ;  its  course 

Huygens,  Constantin,  his  improvements 

and  direction,  147;   most  of  the  new 

in  the  telescope,  02. 
Hvergelmir,  the  caldron-spring  of  the  Ed- 

stars  have  appeared  in  its  neighbor- 
hood, 162. 

da-Songs,  8. 

Morin  proposes  the  application  of  the  tel- 

Indian fiction  regarding  the  stars  of  the 
Southern  hemisphere,  138. 

escope  to  the  discovery  of  the  stars  in 
daylight,  41,  66. 

Indian  theory  of  the  five  elements  (Pant- 

Motion,  proper,  of  the  fixed  stars,  182; 

echota*),  31. 

variability  of,  185,  186. 

Indian  zodiacs,  their  high  antiquity  doubt- 
ful, 121. 

Multiple  stars,  130,  199  ;  variable  bright- 
ness of,  difference  of  opinion  regarding, 
210. 

Jacob,  Capt,  on  the  intensity  of  light  in 
the  Milky  Way.  146;  calculation  of  the 

Nebulas,  probably  closely  crowded  stellar 

orbits  of  double  stars,  by,  211. 
Joannes  Philoponus,  on  gravitation,  18. 
Jupiter's  satellites,  estimate  of  the  magni- 
tudes of,  50;  case  in  which  they  were 
visible  by  the  naked  eye,  52  ;  occulta- 
tious  of,  observed  by  daylight,  62. 

swarms,  37. 
Neptune,  the  planet,  its  orbit  used  as  a 
measure  of  distance  of  61  Cygni,  204. 
New  stars,  151  ;  their  small  number,  151  ; 
Tycho  Brahe's  description  of  one,  152  ; 
its  disappearance,  153  ;  speculations  as 
to  their  origin,  161  :  most  have  appear- 

Kepler, his  approach  to  the  mathematical 
application  of  the  theory  of  gravitation. 
18;  rejects  the  idea  of  solid  orbs,  126. 

ed  near  the  Milky  Way,  162. 
Newton,  embraces  by  his  theory  of  gravi- 
tation the  whole  uranological  portion 

of  the  Cosmos,  21. 

Lalande,  his  Catalogue,  revised  by  Baily, 
115. 

Non-luminous  stars,  problematical  exist- 
ence of,  187. 

VOL   III.— K 


218  INI 

Numerical  results  exceeding  the  grasp 
of  the  comprehension,  furnished  alike 
by  the  minutest  organisms  and  the  so- 
called  fixed  stars,  30  ;  encouraging  views 
on  the  subject,  31. 

Optical  and  physical  double  stars,  200; 
often  confounded,  200. 

Orbits  of  double  stars,  calculation  of  the, 
211  ;  their  great  eccentricity,  211  ;  hy- 
pothesis, that  the  brighter  of  the  two 
stars  is  at  rest,  and  its  companion  re- 
volves about  it,  probably  correct,  and  a 
great  epoch  in  cosmical  knowledge,  212. 

Orion,  the  six  stars  of  the  trapezium  of 
the  nebula  of,  probably  subject  to  pe- 
culiar physical  attraction,  210,  211. 

Pantschata  or  Pantschatra,  the  Indian  the- 

ory of  the  five  elements,  31. 
Parallax,  means  of  discovering  the,  point- 

ed out  by  Galileo,  183  ;  number  of  par- 

allaxes hitherto  discovered,  190  ;  detail 

of  nine  of  the  best  ascertained,  190. 
Penetrating  power  of  the  telescope,  145, 

146. 

Periodically  changeable  stars,  164. 
Periods  within  periods  of  variable  stars, 

168  ;  Argelander  on,  168. 
Peru,  climate  of,  unfavorable  to  astronom- 

ical observations,  103. 
Peters  on  parallax,  192. 
Photometric  relations  of  self-luminous 

bodies,  89  ;  scale,  99. 
Photometry  yet  in  its  infancy,  94  ;  first 

numerical  scale  of,  94  ;  Arago's  meth- 

od, 96. 

Plato  on  ultimate  principles,  12,  13. 
Pleiades,  one  of  the,  invisible  to  the  naked 

eye  of  ordinary  visual  power,  48  ;  de- 

scribed, 141. 
Pliny  estimates  the  number  of  stars  vis- 

ible in  Italy  at  only  1600,  108. 
Poisson,  his  view  of  the  consolidation  of 

the  earth's  strata,  36,  37. 
Polarization  of  light,  45,  47. 
Poles  of  greatest  cold,  36. 
Pouillet's  estimate  of  the  temperature  of 

space,  36. 
Prismatic  spectra,  44  ;  difference  of  the 

dark  lines  of,  45. 
Ptolemy,  his  classification  of  the  stars, 

90  ;  southern  constellations  known  to, 

137. 
Pulkowa,  number  of  multiple  stars  dis- 

covered at,  205,  206. 
Pythagoreans,  mathematical  symbolism 

of  tno,  12. 

Quaternary  systems  of  stars,  210. 

Radiating  heat,  35. 

Ratio  of  various  colors  among  the  mul- 

tiple and  double  stars,  209. 
Rays  of  ftars,  52,  126-128  ;  number  of,  in- 

dicate distances,  128;  disappear  when 

the  star  is  viewed  through  a  very  sma 

aperture,  138,  129. 
Red  stars,  131  ;  varia 


j  Reflecting  sextants  applied  to  the  determ- 
I      ination  of  the  intensity  of  stellar  light. 


1. 
variable  stars  mostly  red, 


Reflecting  and  refracting  telescopes,  63. 
i  Regal  stars  of  the  ancients,  136. 
j  Resisting  medium,  proved   by  observa- 
tions on  Kncke's  and  other  comets,  39. 
Right  ascension,  distribution  of  stars  ac- 
cording to,  by  Schwinck,  140. 
Rings,  colored,  measurement  of  the  in- 
tensity of  light  by,  96. 
Rings,  concentric,  of  stars,  the  hypothesis 
of,  favored  by  the  most  recent  observa- 
!      tions,  149. 
i  Rosse's,  Lord,  his  great  telescope,  65 ;  it* 

services  to  astronomy,  66. 
I  Ruby-colored  stars,  135. 

Saint  Gall,  the  monk  of,  observed  a  new 
j  star  distant  from  the  Milky  Way,  162. 

Saussure  asserts  that  stars  may  be  seen 
in  daylight  on  the  Alps,  57  ;  the  asser- 
tion not  supported  by  other  travelers' 
j  experience,  58. 

Savary,  on  the  application  of  the  aberra- 
tion of  light  to  the  determination  of  the 
parallaxes,  194 ;  an  early  calculator  of 
the  orbits  of  double  stars,  211. 

Schlegel,  A.  W.  von,  probably  mistaken 
as  to  the  high  antiquity  of  the  Indian 
zodiacs,  121 

Schwinck,  distribution  of  the  fixed  stars 
in  his  "  Mappa  coslestis,"  140. 

Scintillation  of  the  stars,  73  ;  variations 
in  its  intensity,  76 ;  mentioned  in  the 
Chinese  records,  77  ;  little  observed  in 
tropical  regions,  77,  78 ;  always  accom- 
panied by  a  change  of  color,  202. 

Seidel,  his  attempt  to  determine  the  quan- 
tities of  light  of  certain  stars  of  the  first 
magnitude,  93. 

Self-luminous  cosmical  bodies,  or  suns, 
199. 

Seneca,  on  discovering  new  planets,  28. 

Simplicius,  the  Eclectic,  contrasts  the  cen- 
tripetal and  centrifugal  forces,  12 ;  his 
vague  view  of  gravitation,  18. 

Sirius,  its  absolute  intensity  of  light,  95 ; 
historically  proved  to  have  changed  its 
color,  131 ;  its  association  with  the  ear- 
liest development  of  civilization  in  the 
valley  of  the  Nile,  133 ;  etymological  re- 
searches concerning,  133,  134. 

Smyth,  Capt  W.  H.,  calculations  of  the 
orbits  of  double  stars  by,  211. 

Smyth,  Piazzi,  on  the  Milky  Way,  146, 
147  ;  on  a  Centauri,  185. 

Sothis,  the  Egyptian  name  of  Sirius,  133, 

South,  Sir  James,  observation  of  380  dou- 
ble stars  by,  in  conjunction  with  Sir 
John  Herschel,  205. 

Southern  constellations  known  to  Ptol- 
emy, 137. 

Southern  Cross,  formerly  visible  on  the 
shores  of  the  Baltic-,  138. 

Southern  hemisphere,  in  parts  remark- 
ably deficient  in  constellations,  112;  dis- 
tances of  its  stars,  first  measured  about 
the  end  of  the  sixteenth  century,  138. 


219 


Space,  conjectures  regarding,  29 ;  com-  |      its  influence 
pared  to  the  mythic  period  of  history,  I      37. 
29;  fallacy  of  attempts  at  measurement  ,  Temporary  stars, 


the  climate  of  the  earth, 

t  of,  155 ;    notoe  to, 

of,  30  ;  po'rtions  between  cosmical  bod-  I      155-160." 
jes  not  void,  31 ;  its  probable  low  tem-    Ternary  stars,  210. 


perature,  35. 

Spectra,  the  prismatic,  44 ;  difference  of 
the  dark  lines  of,  according  to  their 
sources,  45. 

"  Sphtera  aplanes"  of  Macrobiue,  27. 

Spurious  diameter  of  stars,  130. 

Star  of  the  Magi,  Ideler's  explanation  of 
the,  154. 

Star  of  St.  Catharine,  137. 

Star  systems,  partial,  in  which  several 
suns  revolve  about  a  common  center 
of  gravity,  204. 

Stars,  division  into  wandering  and  non- 
wandering,  dates  at  least  from  the  early 
Greek  period,  27 ;  magnitude  and  visi- 


Timur  Ulugh  Beg,  improvements  in  prac- 
tical astronomy  in  the  time  of,  91. 

Translation  in  space  of  the  whole  solar 
system,  195;  first  hinted  by  Bradley, 
195 ;  verified  by  actual  observation  by 
William  Herschel,  196;  Argelander. 
Strove,  and  Gauss's  views,  196. 

Trapezium  in  the  great  nebula  of  Orion, 
investigated  by  Sir  Wm.  Herschel,  203. 

Tycho  Brahe,  his  vivid  description  of  the 
appearance  of  a  new  star,  152 ;  his  the- 
ory of  the  formation  of  such,  154. 


Ultimate  mechanical  cause"  of  all  mo- 
tion, unknown,  24,  25. 

bility  of  the,  48  ;  seen  through  shafts  I  Undulation  of  the  stars,  58,  59. 

of  chimneys,  57 ;  undulation  of  the,  58,  '  Undulations    of  rays   of   light,   various 

59  ;    observation  of,  by  daylight,   66 ;  !      lengths  of,  84. 

scintillation  of  the,  73 ;  variations  in  its    Unity  of  nature  distinctly  taught  by  Aris- 

intensity,  76 ;  the  brightest  the  earliest        totle,  13-15. 

named,  89;  rays  of,  52,  127, 128 ;  color  Uranological  and  telluric  domain  of  the 
Cosmos,  26. 


of,  130  ;  distribution  of,  140 ;  concentric 
rings  of,  149 ;  variable,  161 ;  vanished, 
163 ;  periodically  changeable,  164  ;  non- 
luminous,  of  doubtful  existence,  187 ; 
ratio  of  colored  stars,  209. 

Steinheil's  experiments  on  the  velocity 
of  the  transmission  of  electricity,  87  ; 
his  photometer,  93. 

Stellar  clusters  or  swarms,  140. 

Struve  on  the  velocity  of  light,  82 ;  his 
estimate  of  the  number  of  tine  fixed 
stars,  1 17  ;  on  the  Milky  Way,  139 ;  his 
Dorpat  Tables,  205 ;  on  the  contrasted 
colors  of  multiple  stars,  207  ;  calcula- 
tion of  the  orbits  of  double  stars  by,  211. 

Sun,  the,  described  as  "  a  perpetual  north- 
ern light"  by  Sir  William  Herschel,  34 ; 
in  intensity  of  light  merely  one  of  the 
fainter  fixed  stars,  95 ;  its  place  prob- 
ably in  a  comparatively  desert  region 
of  the  starry  stratum,  and  eccentric,  150. 

Suns,  self-luminous  cosmical  bodies,  199. 


Uranus  observed  as  a  star  by  Flamstead 
and  others,  114. 

Vanished  stars,  163;  statements  about 
such  to  be  received  with  great  caution, 
163. 

Variable  brightness  of  multiple  and  dou- 
ble stars,  209. 

Variable  stars,  160-161 ;  mostly  of  a  red 
color,  165;  irregularity  of  their  periods, 
167  ;  table  of,  172. 

Velocity  of  light,  79 ;  methods  of  determ- 
ining, 80 ;  applied  to  the  determination 
of  the  parallax,  195. 

Visibility  of  objects,  55 ;  how  modified,  56. 

Vision,  natural  and  telescopic.  41 ;  aver- 
age natural,  47,  48;  remarkable  in- 
stances of  acute  natural,  52,  55. 

Wheatstone's  experiments  with  revolv- 
mirrors,45;  velocity  of  electrical 


ing  IT 

light  determined  by,  86." 
Table  of  photometric  arrangement  of  190    White  Ox,  name  given  to  the  nebula  now 
fixed  stars,  100 ;  of  17  stars  of  first  mag-        known  as  one  of  the  Magellanic  clouds, 


nitude,  102;   of  the  variable  stars,  by 


91. 


Argelander,  172,  and   explanatory  re-  Wollaston's  photometric  researches,  95. 

marks,  172-177;  of  ascertained  paral-  Wright,  of  Durham,  his  view  of  the  origin 

laxes,  193  :  of  the  elements  of  the  or-  of  the  form  of  the  Milky  Way,  149. 
bits  of  double  stars,  213. 

Telescope,  the  principle  of,  known  to  the  Yggdrasil,  the  World-tree  of  the  Edda- 

Arabs,  and  probably  to  the  Greeks  and  Songs,  8. 
Romans,   42,    43 ;    di 


:overies   by   its 

means,  61  ;  successive  improvements  '  Zodiac,  period  of  its  introduction  into  the 
Greek  sphere,  119;  its  origin  among  the 
Chaldeans,  120 ;  the  Greeks  borrowed 
from  them  only  the  idea  of  the  division, 
and  filled  its  signs  with  their  own  cataa- 
toriems,  120;  great  antiquity  of  the  In- 


of  the,  62;  enormous  focal  lensrth  of 
som.',  63;   Lord  Rosse's,  65;   Bacon's 
comparison  of,  to  discovery  ships,  130; 
penetrating  power  of  the,  145,  146. 
Telesio,  Bernardino,  of  Cosenza,  his  v: 


of  the 


iews 
phenomena  of  inert  matter,  16. 


Temperature,  low,  of  cclcstiiil 
uncertainty  of  results  "el  obta 


space,  35; 
ained,  36  ; 


dian  ver 


130;  great 
•y  doubtful, 


-ID. 
THE    END. 


Zodiacal  light,  Sir  John  Herschel  on  the, 


A 


if  3 


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